Mitt Romney edges Barack Obama among registered voters in swing states, according to a new Gallup/USA Today poll.  By “edge,” I mean barely edges — by a single point.  Even with that, though, Romney fares far better than his competitors in the same polling:

Republican presidential hopeful Mitt Romney essentially ties Barack Obama in the nation’s key battlegrounds, a USA TODAY/Gallup Swing States survey finds, while rival Newt Gingrich now trails the president by a decisive 14 percentage points.

That reflects a significant decline by the former House speaker since early December, when he led Obama by three points. …

In a head-to-head race, Romney leads Obama by a statistically insignificant percentage point, 48%-47%, the survey finds.

But Obama leads Gingrich, 54%-40%. The president’s standing against him has risen nine points since early December; Gingrich has fallen by eight.

Gingrich fares less well than Texas Rep. Ron Paul, who trails Obama by seven points, 50%-43%, and former Pennsylvania senator Rick Santorum, who also trails by seven points, 51%-44%.

As I’ve written before, this is a bit of an apples-to-oranges comparison.  While the GOP continues its primary slugfest, it’s natural to have some voters refuse to back primary candidates against Obama as a form of principle protest, at least for the moment.  Democrats are united behind Barack Obama and have no such reservations.

The key to this poll is the fact that Obama as incumbent falls below 50%, especially in a poll of registered rather than likely voters, regardless of which head-to-head matchup it appears.  That’s a soft re-elect number — not fatal to re-election at that level, but a problem that could grow after the Republicans actually pick their nominee.  Since likely voter samples tend to produce less favorable results for Democrats, that problem is probably worse than it seems at the moment.

Gingrich still has a problem, though.  Even though he has regained his top-tier status in the Republican primary, he seems to have alienated a lot of voters to have a 17-point swing in the gap over just six or seven weeks.  Given the tone of the campaign and especially Gingrich’s angry attacks over the past week, that may not be a big surprise.  What might play well with the Tea Party base won’t play well in a general election, and the polling results of the last few days indicates that it doesn’t play well with the Tea Party base, either.

That being said, scroll all the way down to look at the sample sizes in the states Gallup polled.  The overall poll is of 737 registered voters, which is a respectable sample size for a national poll, and should be as well for a subset of a national poll.  Some states in this sample only got as few as 11 or 17 voters included in the survey, though.  The participation seems to be proportional to state population sizes, but I think this poll would have benefited from a healthier sample from some of the swing states involved.