Some presidential bids hit the rocks when the married candidate is photographed with a smiling model on his knee. Some when they take an expensive haircut. Others are struck down by an assassin’s bullet. Senator Obama’s dream of entering the White House has turned into a nightmare since the latest unplugged salvo from his wayward guru, the Reverend Jeremiah Wright.

The Reverend Wright stuff appears to vindicate Senator Clinton’s decision to press on regardless of her rival’s lead in delegates, in number of states, and in the popular vote. Her chances of winning the nomination depended upon Mr. Obama stumbling, though few imagined it would be his own pastor who deliberately tripped him. The tortoise is now set to overtake the hare in Indiana on Tuesday, and perhaps in North Carolina as well.

With Mr. Obama beset with troubles that raise profound questions about his judgment, not least in picking advisers fit for the task, Mrs. Clinton’s success should be routine. All delegates should now be having second thoughts. The Reverend Wright has not only made a fool of Mr. Obama but of all his backers.

If Mr. Obama still manages somehow to win his party’s nomination, he would surely go down to defeat in November. As the most senior African-American in Congress, Rep. James Clyburn of South Carolina, put it yesterday, the Reverend Wright is inundating the airwaves with his poisonous rants today so Republican 527 groups won’t have to at the general election.

Yet Mr. Obama has one thing in his favor: the predilection of ideologically driven supporters to fall in love with a losing candidate. The Democratic party’s virgin foot soldiers put more value on intention than achievement and prefer purity to pragmatism. They consider idealistic perfection more important than tainted electability. They are often natural oppositionists who prefer to complain from a position of self-righteous impotence than make the grubby compromises needed to win and to govern.

In 1952, they favored the eloquent intellectual Adlai Stevenson, whose lofty tone, soaring rhetoric, and disinclination to be seen scrapping for the nomination are echoed in Mr. Obama’s languid style. Even though Stevenson lost to Dwight Eisenhower by 442 to 89 electoral college votes, winning just nine states, the purists chose him again in 1956, when he went down to an even more inglorious defeat, with just 73 electoral college votes.

After rejecting the party of Lyndon Johnson and Hubert Humphrey, in 1972 the purists picked the weak, well-meaning peacenik George McGovern and watched him lose catastrophically to Richard Nixon by 520 electoral votes to 17.

The “better lose nobly than win by compromise” syndrome is not confined to the left. In 1964, Republicans, craving a return to full-blooded conservatism after the consensual Eisenhower’s two terms, rejected voter friendly Nelson Rockefeller in favor of the maverick Barry Goldwater.

Johnson beat Goldwater by 486 electoral votes to 52 after swiftboating him with the infamous “daisy chain” ad. It would be 16 years before the genial Ronald Reagan would win on an unalloyed conservative ticket.

The phenomenon is not confined to America. In Britain in 1983, the Labour Party fielded the disheveled leftist intellectual Michael Foot against the pugilistic Margaret Thatcher, with predictable results.

He fought on a manifesto of higher taxation, more nationalization, and nuclear disarmament, described by the member of Parliament, Gerald Kaufman, as “the longest suicide note in history,” and she won in a landslide. Labour languished in opposition until Tony Blair’s hardheaded approach won in 1997.

In France in 2002, the Socialists chose Lionel Jospin, a pragmatic politician par excellence, so adept at acquiring power he even became his perennial opponent President Chirac’s prime minister. The purists on the left detested Mr. Jospin, for his free market economic policies and his ability to hug the middle ground where elections are won and lost, so they mounted a series of debilitating challenges to his leadership.

Mr. Jospin crashed to a crushing defeat, losing to Mr. Chirac for a second time and pushed into a humiliating third place behind the racist Jean-Marie Le Pen. The French left’s untainted brave new world remains on hold to this day.

The Democrats are revealing once again the deep rift in their ranks that emerged at their violent convention in Chicago in 1968. On one side is the coalition that makes up Mr. Obama’s support: impractical students taking part in politics for the first time and the affluent well educated who hanker after the lost idealism of their youth. They are the same groups that in all Western democracies tend to prefer the clean hands of untried optimism to the horny hands of practical politics.

By contrast, Mrs. Clinton, who in Pennsylvania miraculously remade herself as the great-niece of Rosy the Riveter and Norma Rae, attracts blue-collar white men, working women, and those aged over 60. Mrs. Clinton’s working people have little time for what Pat Buchanan calls “faculty lounge” thinking and warm to their candidate’s concentration upon kitchen table issues.

While Mrs. Clinton’s path to the nomination is still cluttered, she has one clear advantage: the 759 super delegates, by definition practical politicians who know there is no such thing as “new politics” and understand the importance of bargaining to get things done. They might recall the words of Adlai Stevenson when told that thinking people supported him. “Yes,” he said, “But I need to win a majority.”

nwapshott@nysun.com