The campaigns of Hillary Rodham Clinton and Barack Obama have been arguing over which candidate is more likely to beat presumptive GOP nominee John McCain in November.

The Clinton campaign, in particular, has argued that the former first lady is the more electable Democrat, an argument the campaign hopes will convince uncommitted superdelegates to back Clinton even if she goes into the party's convention with fewer pledged delegates than her rival, as is likely.

Now the Clinton camp has a fresh piece of evidence to argue its point: A poll out today from the Associated Press-Ipsos found that in head-to-head match ups with McCain, Clinton leads 50 percent to 41 percent. Obama led McCain as well, but by a smaller margin, 46 percent to 44 percent – a virtual tie. Three weeks ago, Clinton led McCain by three points in the poll, and McCain and Obama were tied at 45 percent.

The latest Gallup tracking poll, meanwhile, shows Clinton and Obama in a virtual tie among Democratic and Democratic leaning voters. And a Newsweek poll released over the weekend shows Obama leading Clinton 46 percent to 38 percent. (Obama led Clinton by 19 points in the same poll a week earlier.) Newsweek found that both candidates have a three point edge over McCain in a head-to-head match up.