RICHARD M. Nixon flip-flopped on China. George W. Bush embraced protectionism for the steel industry after preaching free-market principles on the campaign trail. Ronald Reagan failed to remain consistent. In the 1960's he promised not to raise taxes, adding, ''I am in concrete'' for emphasis.

Then, when he became the governor of California in 1970, he raised the tax rate and genially laughed it off. ''That sound you hear,'' he told reporters, ''is the concrete breaking around my feet.''

Among historians, such shifts in opinion -- and the public's willingness to accept them -- inspire little consternation. Reinvention, they argue, is as American as Thanksgiving and jazz. We live in a country, after all, where a Hollywood figures like Samuel Goldwyn and Louis B. Mayer could change things like names and birthdays without being called a traitor to their roots; a place where the cosmetic surgery industry hauls in more than $9 billion a year, and where recreating yourself is a constant theme of drama, music and art. As Walt Whitman, the most American of poets, once wrote:

Do I contradict myself? Very well then I contradict myself, (I am large, I contain multitudes).

In the arts, repeated reinvention is welcomed. 'You're expected to go places you've never been,'' said Jim Guerinot, manager of Beck and No Doubt. Bob Dylan went electric; U2 moved from guitar rock to techno and back again. Ice Cube, one of rap's all-time greats, became an actor. And because negative campaigning rarely exists in pop culture -- you'll never find Eminem calling Josh Groban a ''girlie-man'' -- consistency is rarely an issue.

In today's angry politics, however, change is bad, conversion is good. President Bush's transformation from a frat-boy alcoholic to a teetotaling Christian public servant is believable; so are the multiple epiphanies on race experienced by Gov. George C. Wallace of Alabama, if only because they asked for forgiveness.

The key, says Walter Russell Mead, of the Council on Foreign Relations, -- especially in a country where a Gallup poll found that roughly 40 percent of the population identifies itself as evangelical or ''born again'' -- is to tap into America's tradition of religious reinvention.

''That notion that natural man is full of sin and weak, but that he can be changed through God's intervention, is deeply rooted in American culture,'' Mr. Mead said. ''Even when people are not exclusively religious, we have this notion that you can have a road-to-Damascus experience and radically change.''

David M. Kennedy, author of ''Freedom From Fear,'' a Pulitzer-prize-winning book about the Depression and World War II, made a similar point. He argued that successful flip-floppers have always managed to convince the public that the decision of the moment was incontrovertibly correct. They projected the faith of a zealous apostle, steadfast and stern.

Consider Franklin D. Roosevelt, Mr. Kennedy said. He tacked like a windsurfer on issues of the economy. He cut the federal budget before raising it. In his first inaugural address in 1933, he attacked unscrupulous money-changers, then he forged ties with big business through private-public partnerships, only to later pursue more than 100 companies for violations of antitrust regulations.

''And yet he was strong,'' Mr. Kennedy said. ''He said, 'We have a list of things we'll try, and we'll do them all until the problem is gone.' ''

Senator Kerry, Democrats say, is cut from the same cloth. He seeks results, not ideological purity. His ability to see all sides of an issue is precisely what makes him a compelling leader.

''In a world that changes as quickly as this one does,'' said Michael Feldman, who was chief of staff to former Vice President Al Gore, ''where the facts on the ground can move from minute to minute, I want a commander in chief who can take those changes into consideration before making a decision. I want someone who is decisive but who is willing to have an open mind.''

Democrats also argue that Senator Kerry is being unjustly singled out because he is a legislator with a long history of votes. ''The issues change, the economic issues change, the social environment changes -- and your history is a liability when U.S. senators run for president,'' said Bill Carrick, a Democratic consultant who worked on Representative Richard A. Gephardt's recent presidential campaign.

It is easier than ever to exploit the past as well, Mr. Carrick said. Today's 24-hour news cycle, fused with digital technology, has given journalists an ever-present eye, and the ability to broadcast every shift in phrasing with a simple keystroke.

One look at the Bush-Cheney campaign Web site captures the shift. From the ''Kerry media center'' Web page, it is possible to click through more than 35 of what the site describes as Senator Kerry's flip-flops. There's a ''flip-flop of the day,'' which contrasts Senator Kerry's old statements with those he is making on the campaign trail.

''It used to be possible for candidates to say one thing in Georgia and something else in Ohio and not get called on it,'' said Bruce J. Schulman, a professor at Boston University and the author of ''The 70's: The Great Shift in American Culture, Society and Politics.'' ''That's not possible anymore.''

The role of religion is different too, Mr. Schulman added. ''When Jimmy Carter ran for president, his overt, obvious faith was a source of controversy,'' he said. ''With the famous Playboy interview where he mentions lust in his heart, the whole purpose was to show that it was O.K. and it wasn't scary for him to be so obviously religious.''

Contrast Mr. Carter's experience with the 2000 campaign, when both Mr. Gore and Mr. Bush made conspicuous displays of faith, and Senator Kerry's problem becomes apparent. Reason is slipping, religion is sprinting and Mr. Kerry has bet on the wrong horse. His pragmatic liberalism, says Mr. Schulman, ''doesn't play as well as George Bush's religious conversion.'

Mr. Kerry had his chance to join the converted. According to Mr. Mead, the events of Sept. 11, 2001, could have been the right reason for Senator Kerry to reinvent himself -- to become a flip-flopper that today's fearful, religious voters could really understand.