A month and a half ago, Clinton was widely seen as the inevitable victor. Now, she faces a moment of great peril.

But her spiral downward began with a single mistake in an Oct. 30 debate over a New York state plan to give driver's licenses to illegal immigrants, even as she was coming under more aggressive attack from Obama and John Edwards. The decline affected her standing not only in Iowa, but also in New Hampshire, which was supposed to be Fortress Clinton.

That Clinton is only now rushing to complete visits to all of Iowa's 99 counties reflects the fact that some in her campaign, according to a memo leaked in May, once considered having her skip the state's caucuses altogether. David Bonior, Edwards' campaign manager, said last weekend that Clinton was running behind both his candidate and Obama in many of the state's rural counties.

The Clinton camp believes that Obama and Edwards have gotten a free ride in the last month or so. Clinton's lieutenants and supporters note that while her campaign's attacks on Obama have been roundly criticized, it was Obama who joined Edwards in attacking Clinton first, at little cost.

Nonetheless, the Clinton campaign has had to continue to sow doubts about Obama. Former President Bill Clinton used "The Charlie Rose Show" on Friday to ask if Democrats were willing to "roll the dice" on a candidate with Obama's brief Washington experience. Earlier in the day, Hillary Clinton had said that with her candidacy, "there are no surprises."

Clinton, the Register concluded, was the candidate "best prepared to confront the enormous challenges the nation faces." Obama, it said, was "more inspirational," but "with his relative inexperience, it's hard to feel as confident he could accomplish the daunting agenda that lies ahead." Clinton hopes the endorsement will mark the campaign's next, and last, turning point.

Hillary Clinton's demanding task is to keep doubts about Obama high in the minds of Iowa voters while finding the dash of inspiration that has so far eluded her campaign. Achieving both objectives at the same time will be the greatest challenge of her political life.

By E.J. Dionne, Jr.