PRINCETON, NJ — Barack Obama maintains a lead over John McCain in the latest Gallup Poll Daily tracking update from Saturday through Monday; the size of the lead varies between seven and 10 percentage points among likely voters, depending on turnout assumptions.

Gallup’s modeling of likely voters indicates the race is slightly tighter if we assume that voter turnout patterns will be similar to those seen in most presidential elections from 1952 through 2004. Using this “traditional” definition of likely voters, which takes into account respondents’ history of voting, as well as their current interest in the campaign and self-reported likelihood to vote, Obama leads McCain by seven points, 51% to 44%. This is tied for Obama’s largest lead among this group since Gallup began reporting likely voters in Gallup Poll Daily tracking.

An alternative, expanded likely voter model shows what would happen if turnout reflects voters’ self-reported likelihood to vote and campaign interest, but is not assumed to be dependent on their voting history. Under these assumptions, Obama leads by 10 points, 52% to 42%. — Frank Newport

(Click here to see how the race currently breaks down by demographic subgroup.)