WASHINGTON - Sen. Hillary Clinton's dubious electability has become the overriding issue in the Iowa Democratic caucuses where her chief rival, Sen. Barack Obama, is poised to overtake her on Jan. 3.

The respected Iowa Poll numbers tell the story of the senator's sudden slippage in the crowded race for her party's 2008 presidential nomination. In October, the statewide survey for the Des Moines Register showed her ahead at 29 percent, with former Sen. John Edwards at 23 percent and Obama at 22 percent.

But Sunday's dramatic poll results showed Obama cruising past her with 29 percent, with Clinton dropping back to 25 percent and Edwards standing still at 23 percent.

One poll result was especially damaging to Clinton's prospects in the caucus state: When Democrats were asked which candidate would they be most disappointed to see winning the nomination, Clinton came in first with 27 percent. J. Ann Selzer, director of the Iowa Poll, calls this Clinton's "ick factor."

The Iowa Poll stunned Clinton's high command, and for the first time the former first lady looked vulnerable. By itself, the poll has damaged her candidacy. But earlier polls confirmed what has been happening in the pivotal Midwestern state that could reshape the 2008 campaign.

They reveal an ongoing decline in her support. An American Research Group poll conducted last week showed Obama inching past her, 27 percent to 25 percent. The week before, an ABC News/Washington Post poll had Obama at 30 percent to 25 percent for Clinton.

She was losing ground nationally, too. A USA Today/Gallup Poll reported Monday that support for Clinton has "significantly eroded over the past month."

What has caused this sudden reversal of fortune for the presumptive front-runner? Independent pollsters and some Democrats say it has to do with persistent, lurking questions about her deeply polarizing image and whether, as one Democrat put it, she is "too calculating" for her own good.

Pollster John Zogby, who has been regularly polling in Iowa and the early primary states, tells me her falling numbers stem from party doubts about whether she could win the presidency in November, as well as the growing role of her husband in her campaign and the political baggage of the Clinton presidency.

"There is a perception out there that is raising the question, 'Is she electable?' It's coming up more and more, the closer we get to the Iowa caucuses vote," Zogby said.

"And there is Bill. With Bill out there campaigning, it is raising two important questions. Democrats are asking, 'Do we want to go through all this again?' and 'Who is he campaigning for, her or himself?'"

Notably, Zogby conducted a national poll late last month that found she "would lose to every one of the top-five Republican presidential contenders."

But putting the polls aside for the moment, Democrats have begun to publicly raise troubling questions about her candidacy, a sharp change in the party's reluctance to question her candidacy and her tactics.

In a cover story in the December issue of The American Prospect, a liberal Democratic opinion journal, executive editor Harold Meyerson acknowledges that she "has played 2007 very well," but notes ominously, "the year isn't over yet."

Her evasive, dodging answers to major issues like Social Security, driver's licenses for illegal immigrants and some of her Senate votes "could reinforce the perception that she's too smart by half, too calculating, too triangulating, too -- well, Clintonian," Meyerson said.

"If Obama or Edwards can make this charge stick over the next two months, we may yet have a race," he wrote.

Well, there is no doubt that the Democrats have a race on their hands now. A seasoned, well-grounded candidate might respond to such numbers by raising the importance of the issues that worry voters the most -- but not Clinton. She has chosen to go for Obama's jugular, hurling some of her fiercest attacks of the campaign.

She has begun mocking his experience, accusing him of raising "false hopes" among Democrats, and noting in one attack that he once wrote an essay in elementary school about how he wanted to be president.

"Now the fun begins," Clinton remarked to reporters as she telegraphed her intention to go after Obama with both guns blazing. Obama quietly put her down by saying that launching personal political attacks against one's opponent should not be considered fun. Score that round for Obama.

But what really shook the Clinton campaign to its foundations was the Iowa Poll's finding that she was losing her advantage with women voters. Obama led her among this strategic voting bloc, 31 percent to 26 percent.

It may be too early to say that Clinton is getting desperate. But her wild, scattershot, personally demeaning attacks are beginning to look that way. She is losing it.