"Here are two brother countries, united like a single fist," said socialist Hugo Chávez during a visit to Tehran last November, celebrating his alliance with Islamist Mahmoud Ahmadinejad. Che Guevara's son Camilo, who also visited Tehran last year, declared that his father would have "supported the country in its current struggle against the United States." They followed in the footsteps of Fidel Castro, who in a 2001 visit told his hosts that "Iran and Cuba, in cooperation with each other, can bring America to its knees." For his part, Ilich Ramírez Sánchez ("Carlos the Jackal") wrote in his book L'islam révolutionnaire ("Revolutionary Islam") that "only a coalition of Marxists and Islamists can destroy the United States."

It's not just Latin American leftists who see potential in Islamism. Ken Livingstone, the Trotskyite mayor of London, literally hugged prominent Islamist thinker Yusuf al-Qaradawi. Ramsey Clark, the former U.S. attorney general, visited Ayatollah Khomeini and offered his support. Noam Chomsky, the MIT professor, visited Hezbollah leader Hassan Nasrallah and endorsed Hezbollah's keeping its arms. Ella Vogelaar, the Dutch minister for housing, neighborhoods, and integration, is so sympathetic to Islamism that one critic, the Iranian-born professor Afshin Ellian, has called her "the minister of Islamization."

Dennis Kucinich, during his first presidential campaign in 2004, quoted the Koran and roused a Muslim audience to chant "Allahu akbar" ("God is great") and he even announced, "I keep a copy of the Koran in my office." Spark, youth paper of Britain's Socialist Labour party, praised Asif Mohammed Hanif, the British suicide bomber who attacked a Tel Aviv bar, as a "hero of the revolutionary youth" who had carried out his mission "in the spirit of internationalism." Workers World, an American Communist newspaper, ran an obituary lauding Hezbollah's master terrorist, Imad Mughniyeh.

Some leftists go farther. Several — Carlos the Jackal, Roger Garaudy, Jacques Vergès, Yvonne Ridley, and H. Rap Brown — have actually converted to Islam. Others respond with exhilaration to the violence and brutality of Islamism. German composer Karlheinz Stockhausen termed 9/11 "the greatest work of art for the whole cosmos," while the late American novelist Norman Mailer called its perpetrators "brilliant."

And none of this is new. During the Cold War, Islamists favored the Soviet Union over the United States. As Ayatollah Khomeini put it in 1964, "America is worse than Britain, Britain is worse than America and the Soviet Union is worse than both of them. Each one is worse than the other, each one is more abominable than the other. But today we are concerned with this malicious entity which is America." In 1986, I wrote that "the U.S.S.R. receives but a small fraction of the hatred and venom directed at the United States."

Leftists reciprocated. In 1978-79, the French philosopher Michel Foucault expressed great enthusiasm for the Iranian revolution. Janet Afary and Kevin B. Anderson explain:

Throughout his life, Michel Foucault's concept of authenticity meant looking at situations where people lived dangerously and flirted with death, the site where creativity originated. In the tradition of Friedrich Nietzsche and Georges Bataille, Foucault had embraced the artist who pushed the limits of rationality and he wrote with great passion in defense of irrationalities that broke new boundaries. In 1978, Foucault found such transgressive powers in the revolutionary figure of Ayatollah Khomeini and the millions who risked death as they followed him in the course of the Revolution. He knew that such "limit" experiences could lead to new forms of creativity and he passionately threw in his support.

Another French philosopher, Jean Baudrillard, portrayed Islamists as slaves rebelling against a repressive order. In 1978, Foucault called Ayatollah Khomeini a "saint" and a year later, Jimmy Carter's ambassador to the United Nations, Andrew Young, called him"some kind of saint."

This good will may appear surprising, given the two movements' profound differences. Communists are atheists and leftists secular; Islamists execute atheists and enforce religious law. The Left exalts workers; Islamism privileges Muslims. One dreams of a worker's paradise, the other of a caliphate. Socialists want socialism; Islamists accept the free market. Marxism implies gender equality; Islamism oppresses women. Leftists despise slavery; some Islamists endorse it. As journalist Bret Stephens notes, the Left has devoted "the past four decades championing the very freedoms that Islam most opposes: sexual and reproductive freedoms, gay rights, freedom from religion, pornography and various forms of artistic transgression, pacifism and so on."

These disagreements seem to dwarf the few similarities that Oskar Lafontaine, former chairman of Germany's Social Democratic party, managed to find: "Islam depends on community, which places it in opposition to extreme individualism, which threatens to fail in the West. [In addition,] the devout Muslim is required to share his wealth with others. The leftist also wants to see the strong help the weak."

Why, then, the formation of what David Horowitz calls the Left-Islamist "unholy alliance"? For four main reasons.