The Gallup Organization, in its first measure of the presidential horse race among people most likely to vote, showed Mitt Romney edging in front of President Obama, 49 percent to 47 percent.
The poll, the most robust public, daily tracking poll in the business, is made up of interviews conducted over seven days. The Tuesday result included one day of interviews prior to last week's potentially pivotal presidential debate, one the day of the debate, and five days after it.
The deployment of Gallup's likely-voter model represents the firm's first effort to project the difference between the possible electorate -- that is, all Americans registered to vote -- and the probable electorate that will cast ballots. The gap between the broader universe of all registered voters and those projected by Gallup as likely to vote currently favors Romney, the Republican nominee.
Among all registered voters, Obama actually leads Romney, 49 percent to 46 percent, a net 5-point gap from the likely-voter measure. Why the difference? It's all in how Gallup determines who is a likely voter.
Gallup uses a series of seven questions, including if they voted in previous elections, if they plan to vote this year, and if they know where their polling place is. Those who score highest on these measures are classified as likely voters.
Four years ago, Gallup also offered an expanded likely-voter model, which took into account only whether people said they intended to vote. The purpose of offering that, Gallup wrote at the time was to "take into account higher turnout among groups of voters traditionally less likely to vote, such as young adults and minorities."
Those groups comprised important parts of Obama's coalition; the president won nearly two-thirds of voters under age 30 and 80 percent of nonwhite voters in 2008, according to exit polls. But the gap in Obama's performance between the registered-voter and likely-voter tallies suggests that Obama's voters are not as engaged at this time.
Gallup's editor-in-chief, Frank Newport, wrote on Tuesday that Romney supporters are currently "somewhat more likely to respond that they will definitely vote, that they have thought a lot about the election, and that they are more familiar with where people in their local area vote," compared with Obama supporters. Pew Research Center's Monday release showed a similar gap between registered and likely voters.
Neither Obama's lead among registered voters nor Romney's among likely voters is statistically significant. And there is a silver lining for Obama in the Gallup data. Gallup reported early Monday that, among registered voters, the two candidates were tied in the three days of interviews immediately following the debate that showcased a strong Romney performance and a weak effort by Obama.
But in the two days following those interviews -- Sunday and Monday -- Obama led by 5 points among registered voters, 50 percent to 45 percent. That equals his lead in Gallup polling before the debate -- and suggests that his standing may have, at least temporarily, stabilized following Romney's post-debate surge. In fact, his approval rating among all adults interviewed over the previous three nights sits at 53 percent.
Furthermore, it is not unusual for Gallup to show a significant disparity between likely voters and registered voters. The company debuted its likely-voter model four years ago around the same time in October, and on the first day, it showed Obama leading Sen. John McCain, R-Ariz., by 11 points among registered voters, 52 percent to 41 percent. Among likely voters, Obama's lead was only 50 percent to 45 percent, a net difference of 6 points from the registered-voter results.
Gallup has also tended to show results that were somewhat worse for Obama this year, compared with other pollsters who conduct surveys using live telephone interviews with randomly-contacted respondents.
Gallup interviewed 3,214 registered voters (2,721 of whom were considered likely voters) over the previous seven days, Oct. 2-8. The margin of error for the full rolling sample is plus or minus 2 percentage points.