Eighty-five years ago, in the early morning hours of May 24, 1940, an attempt was made to assassinate Leon Trotsky, the great Marxist revolutionary and co-leader alongside Vladimir Lenin of the October 1917 Russian Revolution. This failed conspiracy was followed by a successful assault by the Stalinist secret police (GPU) agent Ramón Mercader on August 20, 1940.

At around 4:00 a.m. on May 24, 1940, a squad of roughly 20 Stalinist assassins led by the Mexican muralist David Alfaro Siqueiros was admitted to Trotsky’s villa in Coyoacán by the guard on duty, Robert Sheldon Harte, a young member of the Socialist Workers Party (SWP), which was responsible for Trotsky’s security. Disguised as police and armed with submachine guns, automatic rifles and incendiary bombs, the assassins split up into two groups, one tasked with killing Trotsky, the other to attack Trotsky’s guard. They also attempted to destroy Trotsky’s archive, including the uncompleted manuscript of his biography of Stalin.

In an article published shortly after the attack, titled “Stalin Seeks My Death,” Trotsky recounted the horrific events of that morning:

My wife had already jumped from her bed. The shooting continued incessantly. My wife later told me that she helped me to the floor, pushing me into the space between the bed and the wall. This was quite true. She had remained standing, beside the wall, as if to shield me with her body. But by means of whispers and gestures I convinced her to lie flat on the floor. The shots came from all sides, it was difficult to tell just from where. At one point my wife, as she later told me, was able clearly to distinguish spurts of fire from a gun; consequently, the shooting was being done right in the room although we could not see anybody. My impression is that altogether some two hundred shots were fired, of which about one hundred fell right beside us. Splinters of glass from windowpanes and chips from walls flew in all directions. A little later I felt that my right leg had been slightly wounded in two places. 

Having gone through the Russian Revolution and subsequent Civil War, Trotsky was not unfamiliar with gunfire. He and Natalia maintained their composure and lay flat on the ground as the bullets flew past their bodies. Miraculously, neither was killed nor gravely injured. Trotsky recalled that shortly after the assassins left the room, his 14-year-old grandson Seva cried out.

The voice of the child in the darkness under the gunfire remains the most tragic recollection of that night. The boy—after the first shot had cut his bed diagonally as evidenced by marks left on the door and wall—threw himself under the bed. One of the assailants, apparently in a panic, fired into the bed, the bullet passed through the mattress, struck our grandson in the big toe and embedded itself in the floor. The assailants threw two incendiary bombs and left our grandson’s bedroom. Crying, “Grandfather!” he ran after them into the patio, leaving a trail of blood behind him and, under gunfire, rushed into the room of one of the guards.

The assassins knew the precise layout of the Trotsky compound and were clearly assisted by agents from within. Robert Sheldon Harte fled the scene with the assassins, raising suspicions that he was involved in the conspiracy. One month later, on June 25, 1940, Harte’s body was found in a pit, covered with lime and with two bullets in the back of his head. Trotsky, lacking sufficient information, had no way of coming to any conclusion whether Harte was an agent. But in the years and decades that followed, further evidence accumulated, and the release of GPU archives following the dissolution of the Soviet Union in 1991 proved that Harte was a Stalinist agent and played a pivotal role in the May 24 assassination attempt.

In addition to Harte, an even more significant agent was among Trotsky’s guard, as documents were subsequently to establish. While the attack unfolded, all of Trotsky’s guards were rendered ineffective because their guns jammed, having been loaded with the wrong ammunition. The head of security responsible for loading ammunition was SWP member Joseph Hansen, who later informed the FBI that he had been in contact with the GPU as far back as 1938.

The May 24, 1940 attempt to murder Leon Trotsky took place against the background of the opening stages of World War II, which had broken out just eight months earlier on September 1, 1939. The Battle of France was then underway, with French forces surrendering to the Nazis on June 22, 1940.

Trotsky’s assassination on August 20, 1940 was the most consequential political crime of the 20th century. It marked the culmination of a global wave of terror unleashed by Joseph Stalin in the 1930s, when the Stalinist bureaucracy was transformed into an openly counterrevolutionary force. As head of the Soviet bureaucracy which usurped power from the working class, Stalin was determined to destroy all opposition to his dictatorial regime both within and outside the Soviet Union.

In the USSR, the first Moscow Trial of August 1936 initiated the Great Terror, a war launched by the Stalinist bureaucracy against the revolutionary socialist working class and intelligentsia. Between 1936 and 1939, Stalin murdered virtually the entire leadership of the October Revolution, alongside hundreds of thousands of socialists, Marxist intellectuals and workers. Internationally, the Stalinist-controlled Third International (Comintern) consciously betrayed the Spanish Civil War of 1936-39, murdering thousands of their left-wing, socialist and anarchist opponents, including the kidnapping, torture and murder of Andreu Nin, leader of the POUM (Workers’ Party of Marxist Unification).

The Fourth International led by Trotsky was always the central target of this global campaign of political terror. After Lenin’s death, Trotsky led the fight to defend the internationalist principles upon which the Soviet Union had been founded, waging an implacable struggle against the Stalinist bureaucracy and its nationalist program of “socialism in one country.” The Moscow Trials falsely accused Trotsky and his supporters of plotting to assassinate Stalin and other Soviet leaders, collaborating with foreign powers, including Nazi Germany, and aiming to restore capitalism in the USSR. Prior to Trotsky’s murder, the GPU organized the assassinations of several leading figures in the Trotskyist movement, with the agent Mark Zborowski (alias Etienne) at the center of each murder. These included:

1. Erwin Wolf, one of Trotsky’s political secretaries, murdered by the GPU in Spain in the summer of 1937
2. Ignace Reiss, a defector from Stalinism who declared his adherence to the Fourth International, assassinated by the GPU in Switzerland in September 1937
3. Leon Sedov, Trotsky’s son and co-thinker, who died under dubious circumstances in a Paris clinic on February 16, 1938, with all evidence pointing to his murder by the GPU
4. Rudolf Klement, secretary of the Fourth International, abducted in Paris in July 1938 and killed by the GPU, with his dismembered body later found in the River Seine

By 1939, Trotsky was the last surviving leader of the Russian Revolution. Having been expelled from the Russian Communist Party (RCP) in November 1927 and forced into exile from the Soviet Union in February 1929, Trotsky’s life was continuously in danger. Living on, as Trotsky described, “the planet without a visa,” the first eight years of exile were spent in Turkey, France and Norway. He was compelled to leave Europe after Stalin’s initiation of the terror and was only granted asylum by the radical nationalist government of Lázaro Cárdenas in Mexico in December 1936, following an appeal by the socialist painter and sympathizer of Trotsky, Diego Rivera.

Notwithstanding Trotsky’s isolation, Stalin continued to view him as his most dangerous opponent. Especially under conditions of a new imperialist war, the revolutionary potential of the Trotskyist movement to reach a mass audience was ever present. This danger which haunted Stalin was aptly described in 1937 by the revolutionary Victor Serge, using the affectionate name of “Old Man” for Trotsky:

As long as the Old Man lives, there will be no security for the triumphant bureaucracy. One mind of the October revolution remains, and that is the mind of a true leader. At the first shock, the masses will turn towards him. In the third month of a war, when the difficulties begin, nothing will prevent the entire nation from turning to the “organizer of victory.”

Stalin determined that to maintain his power and forestall revolution required that Trotsky be murdered. Recent research has found that the plot to assassinate Trotsky in Mexico was first concretized in the spring of 1939, with GPU agents flooding into the city over the subsequent year. A critical role in preparing the May 24 attack was played by the Mexican Communist Party (PCM), which held an Extraordinary Congress in March 1940 whose central theme was the extermination of Trotskyism. The PCM polluted public opinion in the months prior to the attack with venomous denunciations of Trotsky in their official organ La Voz de Mexico, as well as the publications El Popular and Futuro which they influenced. The primary organizers of the attack, David Alfaro Siqueiros, his brother Alfredo Siqueiros, Antonio Pujol and Pedro Zuniga Camacho, were all members of the PCM.

In Moscow, the failure of the May 24 attack was viewed as a political disaster. According to the former Soviet general and Russian historian Dmitri Volkogonov, “News of the failure of the assassination attempt sent Stalin into a rage,” leading him to decide that “Everything would now be staked on the action of an individual operator who had long been installed in Mexico, and who was preparing to carry out his mission.”

On May 26 or 27, 1940, that operator, Ramón Mercader (aliases Jacques Mornard and Frank Jacson) was first given the assignment to murder Trotsky himself. On the morning of May 28, he was introduced to Trotsky by Sylvia Ageloff, an SWP member who since 1938 had served as Mercader’s liaison with the Trotskyist movement. As documented meticulously in the 2021 series by Eric London, “Sylvia Ageloff and the assassination of Leon Trotsky,” over the next three months Mercader and Ageloff conspired with their GPU handlers based in New York City and Mexico City to carry through the assassination.

Publicly, the Stalinist press deepened their slander campaign against Trotsky, absurdly portraying the May 24 assassination attempt as a “self-assault” somehow organized by Trotsky himself. This brazen lie was parroted by the Mexican bourgeois press and other outlets internationally, despite the total lack of evidence. In response to these slanders, Trotsky spearheaded a vigorous campaign to expose the Stalinist conspiracy against his life. In an article she wrote after Trotsky’s assassination, titled “Father and Son,” Natalia Sedova recalled the period after the May 24 attempt on his life:

At the same time, Lev Davidovich [Trotsky] was taking part in the conduct of the investigation of the case of May 24. Its slothful pace worried LD exceedingly. He followed the developments patiently and tirelessly, explaining the circumstances of the case to the court and to the Press, making superhuman efforts to force himself to refute the self-evident and hopeless lies or malicious equivocations, doing all this with the intense perspicacity peculiar to him, and not allowing a single detail to escape his notice. He attached the proper significance to every single thing, and wove them all into a single whole.

On June 8, 1940, Trotsky published his first statement on the attack, titled “Stalin Seeks My Death.” Debunking the claims of “self-assault,” Trotsky noted:

The accidental failure of the assault, so carefully and so ably prepared, is a serious blow to Stalin. The GPU must rehabilitate itself with Stalin. Stalin must demonstrate his power. A repetition of the attempt is inevitable.

The article documented the vicious public denunciations of Trotsky by leading Mexican Stalinists prior to the assassination attempt, including Vicente Lombardo Toledano, the founder and leader of the Confederation of Mexican Workers (CTM), and Hernán Laborde Rodríguez, the former leader of the Mexican Communist Party (PCM), who despite opposing the assassination plot remained a loyal Stalinist. Concluding the statement, Trotsky wrote:

I live on this earth not in accordance with the rule but as an exception to the rule. In a reactionary epoch such as ours, a revolutionist is compelled to swim against the stream. I am doing this to the best of my ability. The pressure of world reaction has expressed itself perhaps most implacably in my personal fate and the fate of those close to me. I do not at all see in this any merit of mine: this is the result of the interlacing of historical circumstances. But when people of the type of Toledano, Laborde, et al. proclaim me to be a “counter-revolutionist,” I can calmly pass them by, leaving the final verdict to history.

In an August 17, 1940 statement, “The Comintern and the GPU,” published only three days before his assassination, Trotsky elaborated on these themes, while mounting a legal defense of himself and further exposure of the Stalinist plot against his life.

Following the death of Trotsky, no sustained investigation was carried out by the SWP. For decades, the party largely went silent on the matter, failing to probe the dubious connections between Ageloff and Mercader, as well as the broader network of GPU agents who had infiltrated the Trotskyist movement and remained at their posts, including Mark Zborowski in Paris, Sylvia Caldwell in New York City, Joseph Hansen in Mexico City and more. Throughout the Soviet espionage trials of the 1950s and early 1960s, which revealed the machinations of Zborowksi, the Sobolevicius brothers (Jack Soble, alias Senin; and Robert Soblen, alias Roman Well), Sylvia Caldwell (party name used by Sylvia Franklin) and others, the SWP maintained a stony silence in their press.

It was not until 1975, exactly 50 years ago this month, that the International Committee of the Fourth International (ICFI) initiated the first comprehensive investigation into Trotsky’s assassination, under the title Security and the Fourth International. This investigation uncovered numerous concealed facts and brought together all available evidence on both the assassination and the web of Stalinist agents involved in the conspiracy. 

Among the most critical facts were those which shed light on the role played by Zborowski, Hansen, Harte, Caldwell and others whose real history had been covered up or ignored for decades. By that time, the SWP, under the leadership of Hansen, had abandoned Trotskyism. Through Freedom of Information Act (FOIA) requests, the Security investigation learned that starting on August 31, 1940, Hansen initiated relations with the FBI, quickly becoming a double-agent of US imperialism. Starting in the late 1950s, Hansen oversaw the SWP’s transformation into an anti-Trotskyist party flooded with police agents, facilitating the unprincipled reunification with the Pabloites in June 1963. 

The response to Security and the Fourth International by the SWP and all the various Pabloite tendencies amounted to an ever-deepening cover-up of the truth behind Trotsky’s assassination. They all continuously denounced the investigation as “agent-baiting,” while defending proven agents like Harte, Hansen, Caldwell and even Zborowski. In a public statement, they accused the ICFI of “desecrating the grave of Robert Sheldon Harte.”

All of the accusations made by the ICFI were thoroughly substantiated at the time and have only been further vindicated, including through the release of the Soviet spy cables (Venona papers) following the Stalinist dissolution of the USSR in 1991. Despite the definitive proof that Harte, Franklin and others were GPU agents, the SWP and other Pabloite organizations have never admitted to the veracity of the Security investigation, and in fact continue their falsification of the historical record. To this day, a memorial to Harte remains in place at the Trotsky museum in Coyoacán, controlled politically by the Pabloites, who continue to honor the memory of this proven agent.

Over the coming months, the ICFI and World Socialist Web Site will further commemorate the 50th anniversary of the start of Security and the Fourth International, bringing forward the vast body of evidence compiled by the investigation and the far-reaching political conclusions which must be drawn. This legacy, intimately bound up with the central struggle of the 20th century—that between Trotskyism and Stalinism—is indispensable for the political education of a new generation of socialists entering into revolutionary politics today.

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For another detailed account of the May 24 attack, read Part 3 of David North’s essay “Trotsky’s Last Year,” which is also included in the volume Leon Trotsky and the Struggle for Socialism in the Twenty-First Century, available for purchase from Mehring Books.