Barack Obama is leading Hillary Clinton among national Democrats, but the precise nature of Obama's lead appears to be variable. Gallup Poll Daily tracking continues to show a close race, with Obama just a few percentage points ahead, 47% to 45%, in the Feb. 22-24 release. A separate USA Today/Gallup poll conducted Feb. 21-24 shows Obama with a statistically significant lead, 51% to 39%, among national Democrats.
There are some differences in the methodology between these two Gallup polls, including different days of interviewing and some differences in question order. But generally speaking, when Gallup conducts separate polls measuring the same variables at roughly the same times, the estimates are usually and predictably quite similar.
In fact, the USA Today/Gallup poll results and the Gallup Poll Daily tracking results are almost precisely in line with each other on the Republican side: 61% and 63% for John McCain, and 21% and 23% for Mike Huckabee. But this is not so on the Democratic side.
Sampling differences and the impact of random factors inherent in the survey process can sometimes explain why two polls are different. Given the similarities in the two polls' Republican estimates, however, I think the Democratic differences may well be another indicator of the conflicted nature of the Democratic race this year. It's not an easy choice, and as pre-election polls have shown in reference to the actual vote in some of the primary states, there is a lot of volatility out there among Democrats.At the same time, I think a telling question comes from the USA Today/Gallup poll. It asks Americans who they "think will win the Democratic nomination for president this year." The key point: a large majority of Republicans/Republican leaners (82%) and Democrats/Democratic leaners (70%) assume Obama will win the nomination. Even after Obama's big win in Iowa on Jan. 3, a poll that asked the same question showed that 41% of Democrats thought that Obama would win the nomination, while 36% said that Clinton would win the nomination. There's been a lot of change since then.