Conservative Republicans may be wary of Mitt Romney, but the party's moderates appear even more dismissive of his leading conservative rival, Rick Santorum. In fact, a new Pew poll found that 1 in 5 Romney supporters, including independents and some centrist Republicans, would switch sides and vote for President Obama if Santorum became the GOP presidential nominee. Why would they defect? Here, three theories:

1. Santorum is putting ego ahead of party

Santorum is giving moderate Republicans no reason to feel loyal to him, says Jennifer Rubin at The Washington Post. He knows he can't win the delegates he needs to get nominated, so he has the audacity to suggest that God wants a brokered convention so Santorum can sidestep primary voters. Santorum would rather "create chaos and damage his party's prospects for taking the White House than concede" defeat. He's confusing "his own ambitions with what is good for the party," and that doesn't sit kindly with a lot of people.

2. It's just a severe case of primary-season infighting

"There is always some division during a presidential primary," says Jamelle Bouie at The American Prospect. True, "this is more than usual," but during the contentious 2008 Democratic primary, 17 percent of Hillary Clinton's supporters said they wouldn't back Obama. "Of course, when the general election actually came, 89 percent of Democrats voted for Barack Obama," and "I still expect the same" on the GOP side this year.

3. The GOP has split in two

"There really weren't many significant differences" between Obama and Clinton in 2008, says Doug Mataconis at Outside the Beltway. But today, Romney's moderate conservatism stands in "rather stark contrast to the fire and brimstone social conservatism of Rick Santorum." While it is "conceivable that independents and libertarian-minded" Republicans "might be willing to hold their nose and vote for Romney in November, there's no way that such voters are going to vote for Rick Santorum."

