Howard Dean is about to learn one of the cruelest, least-recognized and almost-never-acknowledged lessons of American politics: Most candidates who run for president are diminished by the experience.

There are exceptions, of course, and one of them is still on the trail. He’s Sen. John Edwards, and though he’s not likely to win the Democratic presidential nomination, there is little question that he and his profile have been enhanced by running for president. But many of his colleagues find — or will find — that on the day they leave a presidential race they are enriched but embittered, smarter but somehow smaller.

There are many reasons for this phenomenon, and they help to explain much about our civic life. The pandering — to union officials and business executives, to small-town officials in Iowa and big-mouth activists in New Hampshire, to ethnic panjandrums and Hollywood producers — is undignified.

The pace of the campaign is unforgiving. The price it extracts on spouses, families, the human body and a candidate’s perspective is incalculable. The late Alan Baron, a mad genius from Iowa who helped run Sen. George S. McGovern’s campaign in 1972, used to say the kind of people who run for president are not like other people. They are, he liked to say, a little bit nuts.

Babbit an exception

Which is why one of the few candidates to leave a presidential campaign bigger than he was when he began it was Bruce Babbitt of Arizona, who unsuccessfully sought the Democratic nomination in 1988.

“Bruce Babbitt is the most thoroughly normal person who ever ran for president, which of course was one of his disadvantages as a candidate,” said Michael D. McCurry, who served as Babbitt’s campaign press secretary and was also involved in the presidential campaigns of John H. Glenn Jr., Bob Kerrey and Bill Clinton. “But in the process of running, he found a voice for himself.”

That seems to be happening for Edwards, who may emerge as a logical running mate for Sen. John F. Kerry if the Massachusetts senator wraps up the Democratic nomination. Edwards’ “two Americas” critique is not original — the socialist writer Michael Harrington made much the same argument in his “The Other America,” published in 1962, admired by President John F. Kennedy and read by thousands of college students since — but the North Carolina lawmaker delivers the message with unusual, special force. He’s grown on the trail, and his aura has grown as well.

Race diminishes Dean

The same cannot be said for Dean, the former Vermont governor who remains in the presidential race with diminished influence, diminished rhetorical power and diminished stature. He’s likely to be remembered less for the movement, however fleeting, that he created than for the spectacle that he, and the cable networks that aired the episode repeatedly, created with his concession speech in Iowa.

But though his rise and fall were both unusually swift, Dean’s fate is not unusual. Presidential campaigns — humbling experiences for nearly everybody but the late Hubert H. Humphrey, who spoke of the politics of joy — eat candidates.

Walter F. Mondale was a leading lawmaker, a pioneering vice president, and the heir to a distinguished strain of Minnesota progressivism. Today, he is remembered as the man who lost as many states as McGovern. Robert J. Dole was a portrait in courage and determination, a crusader for food for the hungry and rights for the disabled and, along with Lyndon B. Johnson, perhaps the finest legislator of the 20th century. Today he is remembered as the man whose favorite campaign riposte was “whatever.”

Tank ride dogs Dukakis

Michael S. Dukakis served as governor of Massachusetts for a dozen years, helped the state make the transition from the old economy to the new, and won a presidential nomination that no one remotely dreamed he could capture. Today Dukakis, whose 16 months of Army duty in South Korea give him more real military experience than war presidents Abraham Lincoln, Woodrow Wilson, Franklin D. Roosevelt and George W. Bush combined, is remembered as the guy who looked like a goofball in a tank.

George W. Romney — the head of American Motors Corp. and a three-term governor of Michigan — was nobody’s fool, unless you were devoted to the Nash and Hudson lines, which Romney’s AMC dropped in 1957. But he entered the race for the 1968 GOP presidential nomination, returned from Vietnam, and said he had been “brainwashed.” He spent the rest of his career, which included a stint as secretary of housing and urban development, trying to live down the remark, which had been intended to underline the deceit of American military and diplomatic personnel, not the limits of his own intelligence.

One more example should make the point: Does anyone today remember Edmund S. Muskie as secretary of state? He’s recalled as the sharp-tempered, overly emotional wreck of a one-time front-runner from Rumford, Maine, who cried in front of the Manchester Union Leader in the winter of 1972, a terrific tale but, according to some witnesses who insist that his face was full of snowflakes and not tears, maybe not true at all.

Mondale knows this syndrome all too well. Many years ago he ran into McGovern and asked him how long it takes for the hurt of a landslide defeat to wear off. McGovern’s answer: I’ll call you when it happens.

John Kennedy once told the television journalist Sander Vanocur that “victory has a hundred fathers and defeat is an orphan.” Here’s a sobering truth for anyone contemplating a presidential race — and for anyone who, like Kerry, is poised to win a presidential nomination: In politics, that orphan has plenty of company, and plenty of wounds.

David Shribman is a columnist for Universal Press Syndicate.