So now there is a front-runner. By virtue of mathematics (the money he has raised) and chemistry (the way his rivals treat him), former Gov. Mitt Romney of Massachusetts is the leading candidate for the Republican presidential nomination.

There's danger in that position. The GOP field didn't gang up on Romney in their New Hampshire debate last week, but that's only because many of the candidates are just getting their campaign legs and are breathing the sweet air of being in presidential politics for the first time.

Once they feel their political survival is at stake, their restraint will disappear, and one after another they will send arrows Romney's way. Those arrows will provide opportunities for fellow contenders -- and will challenge Romney's mettle, providing evidence that he is strong enough to engage President Barack Obama in the general election or raising questions about his suitability as the party nominee.

Sometimes front-runners stumble. Democrat Gary Hart did in 1988, for example, but Hart's fall was more a matter of personal conduct than political profile.

Hart was in many ways ideally suited for his party at the end of the Reagan era. He was a westerner, an apostle of new ideas, no stranger to military issues, nimble in debates and stentorian on the stump. His fall, after an apparent affair with a young woman, was one of the political benchmarks of the era, removing the press's hesitancy to examine the personal lives of politicians and postponing the Democrats in their effort to sculpt a new image for themselves.

Despite the perils in leading the pack, though, it's a lot better to be the front-runner than one of the other contenders. More often than not, front-runners prevail and win their party's nomination: Walter F. Mondale in 1984, George H.W. Bush in 1988, Robert J. Dole in 1996, George W. Bush and Albert Gore Jr. in 2000 are among many examples.

This pattern is particularly strong among Republicans, who, at least in presidential politics, are temperamentally more inclined to respect customary lines of authority and the prerogatives of party elders. Three of their last four elected presidents were respected party figures who had run for the White House before, and the fourth (George W. Bush) was the son of a president, the grandson of a senator, the brother of a governor and himself the governor of the largest state headed by a Republican. Indeed, every Republican nominee for the past four decades, with the exception of Bush and Gerald R. Ford, an appointed but incumbent president, had run for president before.

This factor, along with Romney's bulging campaign treasury and the deference the other candidates displayed last week, underlines Romney's position -- a position so commanding that he actually outpolled Obama in the latest Washington Post-ABC News Poll. Indeed, Romney has more than four times as much support in New Hampshire as his nearest rival, former New York Mayor Rudolph Giuliani, who isn't even in the race (yet).

New Hampshire is vital for Romney, who owns a vacation home in the state and whose primary residence is in a neighboring state. His defeat there four years ago at the hands of Sen. John McCain represented a substantial repudiation, as Massachusetts politicians from John F. Kennedy's time on have prevailed in New Hampshire -- including Ambassador Henry Cabot Lodge (1964), who didn't even campaign and managed to beat Sen. Barry Goldwater and Gov. Nelson A. Rockefeller in a remarkable write-in effort, and former Sen. Paul E. Tsongas (1992). The only exception, besides Romney, was Edward M. Kennedy, who was defeated by an incumbent president, Jimmy Carter, in 1980.