The closer John McCain has come to winning the Republican presidential nomination, the more Senator Barack Obama has trumpeted his own electability, arguing that his broad appeal would allow him to challenge the Arizona senator in a way Democratic rival Hillary Clinton could not.
"I'm confident I will get her voters if I'm the nominee," Obama told reporters this month. "It's not clear that she would get the voters I got if she were the nominee."
But a review of exit polling data from states that have held primaries suggests that Obama may be overstating his case.
More than 21,000 Democratic voters in 19 states have been surveyed on whether they would be satisfied with Clinton or Obama as the nominee, regardless of how they voted. The results for the two candidates are virtually indistinguishable: Roughly half of voters, on average, said they would be satisfied with Obama or Clinton, with about a quarter of voters saying they would be happy only with Obama, and a quarter saying they would be happy only with Clinton.
An analysis of exit polls from Super Tuesday indicates that Obama voters were slightly more accepting of Clinton as their nominee than Clinton voters were of Obama as theirs: Fifty-two percent of those who voted for Obama on Feb. 5 said they would be satisfied if Clinton won the nomination, while 49 percent of Clinton voters said they would be satisfied if Obama did.
"Sure, there are some true believers who don't like the other candidate," said John Della Volpe, director of polling at Harvard University's Institute of Politics. "By and large, I think Democratic voters understand that it's bigger than just one of these two guys."
The exit polls provide only a snapshot of the views of Democratic voters. And the same exit polling, conducted by Edison Media Research and Mitofsky International for the TV networks and other media organizations, was not done in states that held caucuses instead of primaries. Those are states where Obama has done particularly well and where, his campaign argues, some of his most pivotal supporters - independents, Republicans, and conservative-leaning Democrats - reside.
But the caucuses drew far fewer voters than the millions who voted in the primaries, and several of the caucus states are historically Republican states that will be difficult for any Democrat to win in the general election.
Obama and his campaign contend that he is largely fueling the record voter turnout in nearly every Democratic primary or caucus so far. Many of those voters, they say, have been motivated to vote exclusively by Obama's candidacy and will not necessarily return to the polls on Nov. 4 if Clinton leads the ticket.
Steve Hildebrand, Obama's deputy campaign manager, said he could not explain why exit polling did not reflect that assertion. Hildebrand said Obama is basing his argument about electability largely on his appeal among independents and moderate Republicans, which has helped fuel Obama's overwhelming victories in states such as Virginia.
"Right now we've got the benefit that a majority of American voters plan to vote Democratic," Hildebrand said in a telephone interview Friday. "And the risk involved in that is whether John McCain, as someone who has had an appeal to independent voters, whether or not he's going to be able to over time take that Democratic advantage away."
A Cook Political Report/RT Strategies poll of registered voters this month found that Obama would fare better against McCain than would Clinton, largely because he would draw significantly more independents and Republicans than she would.
Beyond arguing that his supporters might not vote for Clinton, Obama also asserts that he would be a stronger candidate against McCain because he is less tied to Washington and because he, unlike Clinton, opposed the Iraq war from the start.
It is undeniable that Obama has attracted countless new voters around the country, many of whom have said in interviews that he has stirred excitement in them in a way no politician has in years, if ever.
"For a person of my age, it's bringing back all of the juices," said Maryann Cool, a 52-year-old teacher from East Orange, N.J., who said she just "gave up" on politics.
Obama has cited his ability to draw such new faces in arguing that he is expanding the pool of voters and thus better positioned not just to win in November, but also to govern with a "new American majority."
"We can't start off just with the same playing field and expect to win," he told reporters in Los Angeles on Feb. 1. "We've got to broaden the playing field. We've got to expand the electoral map."
But while voters weren't directly asked whether they would vote in the fall only for their favored candidate, there's no evidence from the exit polls indicating that Obama's voters would abandon Clinton were she to win the nomination.
On average, 24 percent of Democratic voters from the 19 states where exit polls asked the question said they would only be satisfied with Clinton; 23 percent of voters said they would only be content with Obama.
Not surprisingly, voters in states where Obama won by the biggest margins were more likely to say they would only be satisfied with him as the nominee. In Virginia, 34 percent of Democratic voters said they would only be content with Obama, compared with 15 percent who said they would only be happy if Clinton won, exit polls show. In each contender's home state - Illinois for Obama, New York for Clinton - voters were far more likely to say they would only be satisfied with the hometown candidate.
In other states, however, the margins were much smaller. Obama won Delaware and Alabama on Super Tuesday, for example, but voters in those states were slightly more likely to say they would be satisfied only with Clinton than only with Obama.
"I'm wondering if he's even consulting polls to make that claim, or just kind of trying to make that become a reality at the moment because he has the momentum," said Diana Owen, an associate professor of political science at Georgetown University and chairwoman of the school's American Studies program.
Scott Helman can be reached at email@example.com.