The liberalism of American Jews is as stubborn as it is longstanding. Jews have voted Democratic in every presidential election since 1928, and, with the exception of Jimmy Carter in 1980, no Democrat in all those decades has attracted less than 60 percent of the Jewish vote. The average has been closer to 75 percent.

Last November, 78 percent of American Jews voted for Barack Obama. That was 25 percentage points higher than the 53 percent he drew from the electorate as a whole, and 35 points higher than the pro-Obama white vote of 43 percent. Not even Hispanics, who gave Obama 67 percent of their vote, surpassed Jewish voters in supporting the Democratic nominee.

It isn’t only on Election Day that American Jews lean so strikingly to the left side of the argument.

On issue after issue, Jews are far more likely than other Americans to embrace liberal positions. More than 80 percent oppose prayer in public schools, for example, while only 38 percent of non-Jews feel the same way. Three-fourths tell pollsters they want more government spending on health, education, and the environment; among non-Jews the figure is 57 percent. On race, abortion, the military, civil liberties, marijuana, euthanasia, gun control - name almost any controversial political issue - American Jews can be trusted to come down firmly and disproportionately on the left.

Why?

This persistent liberalism perplexes many non-Jews and non-liberals. Why should Jewish Americans be so out of step with their socioeconomic peers? And why, they ask, do Jews remain so loyal to the left when hostility to Jews and to the Jewish state is increasingly a left-wing phenomenon, and when the right - especially the Christian right - has become a bulwark of support for Israel and the Jewish people?

“I cannot remember ever being asked any question as often as I have been asked why so many Jews continue clinging to the Left and why they still vote as heavily as ever for the Democratic Party,” writes Norman Podhoretz, the former editor-in-chief of Commentary and one of America’s leading public intellectuals. “Usually I respond by saying that it is a very long and very complicated story.” In “Why Are Jews Liberals?” he sets out to tell that story, and does so with insight and verve.

Podhoretz is known today as a founding father of neoconservatism. But he began as a committed liberal who underwent a metamorphosis. A radical stalwart in the 1960s, Podhoretz began moving rightward a decade later, repelled as much by the “open expression of hostility to Jews” that he encountered in the New Left as by its apparent growing contempt for traditional American values and institutions.

Few in the Jewish community, however, followed Podhoretz across the ideological divide. Evidence and argumentation have failed to budge what Podhoretz calls “the stubborn Jewish refusal to rethink the old political pieties.”

For a long time, those “pieties” had made sense. Podhoretz spends the first half of “Why Are Jews Liberals?” briskly surveying 2,000 years of Jewish history, from the birth of Christianity in the Roman era to the defeat of Hubert Humphrey in 1968. It was that history, he explains, that forged Jewish liberalism. Time and again during those 20 centuries Jews had suffered persecution and ostracism in a number of nations, and time and again the most hostile elements of society had also been the most conservative and/or Christian. Jews reasonably internalized an intense aversion to what came to be known as the right, the source of so much that had sought to destroy Jewish life: medieval blood libels, czarist pogroms, Nazism.

Even in the United States, which in many ways represented a break with this history, there was much to reinforce Jewish antagonism toward the right. It was conservative isolationists like Charles Lindbergh, for instance, who strove to keep the United States from going to war against Hitler. And it was Franklin Delano Roosevelt, a liberal Democrat, who led the coalition that destroyed Nazi Germany and ended the Holocaust. It would have been strange if Jews hadn’t felt an abiding loyalty to the Democratic Party - a loyalty that only intensified when FDR’s successor, Harry Truman, overrode the objections of the State Department and recognized the newborn state of Israel just minutes after its proclamation on May 14, 1948.

But the world has changed, Podhoretz argues in the book’s second half, and Jews should change with it. Numerous polls confirm that support for Israel today is far stronger among Republicans and conservatives than among Democrats and liberals. And while the right has grown far less willing to tolerate anti-Semites in its midst, much of the left has gotten more comfortable with anti-Semitism - especially the variety that expresses itself in malignance for the Jewish state.

But he writes knowing that he will not be heeded. American Jews cling to liberalism, he concludes, because it has superseded Judaism as their religion - or because they have come to regard Judaism as “liberalism by another name.” Doubtless that is an assertion many Jewish liberals will scorn. But then, scorn from the left has never kept the author of “Breaking Ranks” and “Ex-Friends” from speaking bluntly about politics and ideas.

Like its author, this cogent book is pugnacious and perceptive, and even readers who don’t share Podhoretz’s politics will find his analysis thought-provoking. “Why Are Jews Liberals?” may not change many votes, but it sheds new light on an intriguing enigma.