Of all the signs of movement in Obama’s direction, Gallup's poll is perhaps the single most telling. With huge sample sizes, Gallup's demographic breakdowns have much smaller margins of error than other polls.

Today Gallup released its weekly demographic breakdown, which covers the last four weeks of Gallup polling. Over that period, Obama led 48-45 compared to a one point deficit over the prior four week period (Obama was on average up by 1 prior to the DNC; he leads by about 6 over the last week). In the survey, there were hints of an important shift:

The number of non-white voters who said they would “definitely vote” increased to record highs. 81 percent of African Americans said they would “definitely vote” compared to 82 percent of whites—the smallest deficit to date. In total, 75 percent of non-white voters said they would definitely vote compared to a low of 68 in July. Only one quarter of the sample reflects the DNC, so it will be interesting to see if these numbers increase further over the coming weeks.

Given the tremendous gap in the voting preferences of white and non-white voters (Obama leads among non-white voters 78-15 but Romney is ahead 54-39 among white voters), these changes are potentially very significant. If the only voters who turned out were those who say they would “definitely vote,” then Obama’s 3 point lead among registered voters would shrink to 1.8 points. But that 1.2 point gap represents an improvement from last month's 2.2 point gap since just 68 percent of non-white voters said they would definitely vote, compared to 80 percent of white voters.