A new Des Moines Register poll shows that support among the state's GOP caucus-goers has plummeted to 8 percent, which some pundits are saying signals the end for the former pizza executive. The Register, which took the poll from November 27-30, shows that the 24 percent Cain enjoyed in late October at the height of his surge as the latest anti-Romney has virtually evaporated. Iowa, which once looked like one of the strongest early-primary state for Cain, is slipping out of his reach -- and political watchers are noticing the nosedive (illustrated right there on the Register's front page). Alexander Burns of Politico writes that the "numbers for Cain signal a major — though not really surprising — shakeup in the Iowa race."  Business Insider is more emphatic: "With success in Iowa off the table, let the Cain deathwatch begin."

The poll identified two factors depressing Cain's popularity. First of course are the sexual abuse allegations, which the Register could watch drain support from Cain in realtime. Over the course of the four-day polling period, news of Ginger White's 13-year affair with Cain broke. So:

On a question about the candidate most likely to have a scandal in the White House, Cain’s numbers rose from 25 percent at the start of polling, then to 36 percent, and to 47 percent at the end of polling.

The second is even more substantive: voters are concluding that in addition to being a philanderer, he also doesn't have a grasp of the issues. 27 percent of caucus-goers call him the least knowledge GOP candidate. So as some are joking, Cain's in first place at least in that regard. Tweets The New York Times' Jeff Zeleny:

Meanwhile, Cain set a Monday deadline for him to make the decision to stay in the race, reports Politico.