Obama could have a bigger lead if he convinced more people to vote. Meanwhile, a national poll is showing virtually no bump for Romney following his veep choice, while a swing state poll shows just a little one. Here's our guide to today's polls and why they matter.

Findings: Of unregistered voters, 43 percent said they would vote for Obama and 23 percent said they would vote for a third party candidate over Romney. Obama also won 43 percent of voters who are registered, but "said they are less likely to cast a ballot." Romney got 20 percent of that category and 18 percent wanted a third party candidate.
Pollster: USA Today/Suffolk University
Methodology: Live telephone interviews with 800 U.S. adults with a margin of error of +/-3.47 percent. 
Why it matters: According to USA Today, this year "perhaps 90 million Americans who could vote won't." Based on these results if Obama could just get them out to vote he would have a much handier win than he does right now. 
Caveat: In the poll, more of the registered voters polled were Democrats: 30 percent to Republicans' 14 percent. 


Findings: In the four days before Mitt Romney announced Paul Ryan as his running mate he polled 46 percent to Obama's 45 percent in the Gallup Daily tracking poll. In the four days after he gained one percentage point. 
Pollster: Gallup
Methodology: For the after results: telephone interviews with 1,863 registered voters August 11 through 14 with a margin of error of +/-3 percentage points with "95% confidence." 
Why it matters: Well, not much, yet. Gallup writes that the announcement "has not done much to change voter preferences, at least initially," the Los Angeles Times' David Lauter points out. "[I]t’s important to remember two facts: Vice presidential picks often don’t generate much movement in polls, and in this campaign, with so few undecided voters and both sides heavily dug in, a big shift for either candidate would constitute a major surprise." 

Caveat: Lauter also noted that Gallup tracking and an Economist/YouGov survey, which also showed little post-veep pick movement, have "generally shown more favorable numbers for Romney than most." 


Findings: A poll of swing states shows Romney and Ryan with a single point lead over the incumbents: 47 percent to 46 percent. In a July edition of this poll Obama led by two points. Since  July Romney has gained in Ohio and Virginia, while Obama has done so in Colorado and Florida. 
Pollster: Purple Insights
Methodology: Automated interviews with 1,000 likely voters in Colorado, Florida, Iowa, Minnesota, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia, and Wisconsin August 13 through 14 with a margin of error of +/-3.1 percent. Oversample of Ohio, Virginia, Florida, and Colorado with a margin of error of +/-4.0 percent. 
Why it matters: The poll attributes a "small bump in the immediate aftermath of the Ryan announcement." Though small, "it is also the first sign of positive momentum for the Romney campaign that we’ve seen in the PurplePoll in the last few months." These are the states Obama won in 2008, and The Hill explains he will "need to win about half of these in 2012 to secure reelection.

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Caveat: All the candidates for president and vice president are viewed as  more unfavorable than favorable except for Paul Ryan. Romney however gained in favorability since the last poll.