The Friday-Sunday poll, mostly conducted as Obama was returning from his much-publicized overseas trip and released just this hour, shows McCain now ahead 49%-45% among voters that Gallup believes are most likely to go to the polls in November. In late June, he was behind among likely voters, 50%-44%. Among registered voters, McCain still trails Obama, but by less. He is behind by 3 percentage points in the new poll (47%-44%) vs. a 6-point disadvantage (48%-42%) in late June.

Results based on the survey of 791 likely voters have margins of error of +/- 4 percentage points -- so McCain's lead is not outside that range. Results based on the survey of 900 registered voters also have margins of error of +/- 4 percentage points. Gallup editor Frank Newport tells Jill that "registered voters are much more important at the moment," because Election Day is still 100 days away, but that the likely-voter result suggests that it may be possible for McCain to energize Republicans and turn them out this fall.

Who is a likely voter? In this poll, Frank says, that was determined by how much thought people have given to the election, how often they say they vote and whether they plan to vote in the election in November. He says the number of likely GOP voters is up for now, probably in part because of Obama's trip and the "laudatory" media coverage of it. "At least in the short term it may have had the side effect of energizing Republicans," he says. Also, he says that McCain's sharp words about Obama and the media last week may have energized his faithful.