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." Continued...