Via Mark Halperin, the latest USA Today/Gallup poll has John McCain leading Barack Obama by 49-45 amongst likely voters. The poll actually shows the Arizona senator gaining by 10 points since last month alone.

Republican presidential candidate John McCain moved from being behind by 6 points among “likely” voters a month ago to a 4-point lead over Democrat Barack Obama among that group in the latest USA TODAY/Gallup Poll. McCain still trails slightly among the broader universe of “registered” voters. By both measures, the race is tight.

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%.

McCain still trails amongst registered voters, but by less than before. He had a 6-point disadvantage in June, but the latest poll shows him behind by just 3. What defines a “likely” voter as opposed to a “registered” 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.

Gallup has also seen a rise in the number of likely GOP voters. The organization attributes that to Obama’s world tour, and I’m not so quick to disagree.