Most Iowa Democrats say the fact that Clinton would be the first woman president doesn't directly influence their choice; however among women 19 percent, nearly one in five, say it does make them more likely to support her.
Apart from women, Obama does notably better, and Clinton less well, among independents rather than registered Democrats (35 percent of independents support Obama vs. 18 percent for Clinton). That's potentially a challenge for him because it can be tougher to get independents to turn out.
Similarly, Obama does better among younger Iowans, and also among those who say it'll be their first caucus (about a third of all likely caucus-goers). Clinton, however, also does better among first-timers; she needs their turnout as much as Obama does, or more.
The edge turns to Obama among the most highly educated voters, a reliably high turnout group; he has 37 percent among those who've done post-graduate work (a fifth of all likely caucus-goers) vs. just 16 percent for Clinton, her weakest education group by far.
Perhaps the largest change in any individual groups has been at Edwards' expense -- a drop in support among older voters in Iowa, which had been his best group. Among those age 65 and over, just 18 percent now support him, down from 36 percent in July. Among seniors -- another normally high-turnout group -- Clinton now leads.
A final change in Iowa, less fortuitous for Clinton, is among political moderates; her support in this group has slipped to 19 percent, again in third place behind Obama and Edwards. She does better with liberals, but there are fewer of them.
SAMPLING and TURNOUT -- Turnout matters especially in low-attendance events like caucuses. This poll was conducted by telephone calls to a random sample of Iowa homes with landline phone service. Adults identified as likely caucus-goers account for 14 percent of respondents; the subgroup of those who say they're certain to attend account for just under 9 percent (with, as noted, no significant change in results). These compare to turnout in 2004 of 5 percent of the state's voting-age population.
METHODOLOGY -- This ABC News/Washington Post poll was conducted by telephone Nov. 14-18, 2007, among a random sample of 500 Iowan adults likely to vote in the 2008 Democratic presidential caucus. The results have a 4.5-point error margin. Sampling, data collection and tabulation by TNS of Horsham, Pa.