Obama leads in key swing states, new polls find Two of the states are familiar bellwethers, the third a relative newcomer to the swing state category. For either Mitt Romney or President Obama, a clean sweep would guarantee victory on Election Night. And, for the moment, it's Obama with the advantage in Ohio, Florida and Virginia, according to a new round of polls from NBC News and Marist. In Florida and Virginia, Obama leads 48% to 44%. In Ohio, Obama's lead is 48% to 42%. The margin, though, has narrowed in each since Romney essentially clinched the Republican nomination, and will likely continue to fluctuate as both campaigns start honing their general election messages there. The fact that Obama's standing is just shy of the key 50% threshold shows how he still has work to do making his case. For the moment, voters in each state are giving the president the benefit of the doubt on the economy. Voters narrowly give him a positive grade in handling the economy, and by a more sizable margin say the lingering problems are ones he inherited, not ones that resulted from his policies. The notion that his policies have actively aided the recovery may explain the wider lead in Ohio, where Democrats say one in eight jobs is tied to the auto industry. Discussing the results of the new polls, NBC's Chuck Todd offered a word of caution: the results are closer among voters who they consider more likely to turn out on Election Day. The partisan breakdown of the polling sample, each of about 1,100 registered voters, also plays a role. Case in point: another poll of Florida released this week, by Quinnipiac University, showed Romney ahead 47% to 41%. That sample included more registered Republicans than Democrats; the NBC/Marist poll had more Democrats than Republicans. Which poll is "right" about the partisan split? The truth is, no one knows. In 2008, Democrats turned out heavily not just in Florida, but across the country, helping Obama carry states that his party had lost in previous elections. In 2010, it was Republicans" turn to dominate the turnout as many Democrats stayed home. The difference between the two polls just hammers home a truism about close elections - turnout matters. David Lauter contributed to this post.