Which GOP rivals would vote for Ron Paul if he's GOP nominee?

With libertarian-leaning Ron Paul riding high in polls of Republican voters in Iowa, a simple question has become a hot one in recent days for his rivals in the presidential race: If the Texas congressman were to win the Republican nomination, would they vote for him?

So far Mitt Romney and Rick Santorum have said yes.

Newt Gingrich has said no.

And all six of Representative Paul's rivals have strongly criticized his views, notably on foreign policy.

On Wednesday, former Massachusetts Governor Romney, the other candidate at the top of polling in Iowa, weighed in with a yes.

“I’ve already crossed that river, if you will, by saying [in Republican debates] ... that all of the people on stage would be superior to the president we have,” Romney told CNN interviewer Wolf Blitzer. “So yes, I would vote for him.”

On Friday, however, Mr. Romney sounded decidedly less enthusiastic, while stopping short of reversing his position. "I don't think Ron Paul represents the mainstream," he said. "I'm working harder than anyone to make sure he's not the nominee."

Romney's use of "mainstream" echoed another GOP candidate, former House Speaker Gingrich, who gave a flat "no" when asked if he could vote for Paul.

"I think Ron Paul's views are totally outside the mainstream of every decent American," Gingrich said Tuesday in his own chat with Mr. Blitzer. "There will come a morning when people won't take him as a serious person."

Gingrich said Paul had allowed "racist" content to go out in newsletters bearing his name, is "a person who thinks the United States was responsible for 9/11," and is "a person who believes it doesn't matter if the Iranians have a nuclear weapon."

At the same time, Gingrich didn't commit his vote when asked to make a choice between Paul and Barack Obama. He referred to President Obama as "very destructive to the future of the United States."

All the other Republican candidates have stood at odds with Paul on foreign policy, where he supports noninterventionism and a pullback of American military presence worldwide.

Paul links his positions both to the financial toll of rising national debt and to what he calls failed foreign policies. In one recent debate, he commented on the threat of Islamic terrorism: "There are some radicals. But they don't come here to kill us because we're free and prosperous.... The CIA has explained it to us. They said they come here and want to do us harm because we're bombing them."

Paul has drawn strong support from libertarian-leaning Republicans and independents, and attention to his candidacy has grown in recent days as polls show him within striking distance of a win in the Iowa caucuses Jan. 3.

While saying he could vote for Paul, Romney added that “I don’t agree with a lot of the things that Ron Paul says and I would vehemently oppose many of his initiatives." He voiced the expectation that if nominated by the party, Paul could be moved “in a direction that’s more productive.”

That may be wishful thinking on Romney's part, since Paul has staked his candidacy on a reputation for unyielding principles. But Romney and the other Republicans say talk of Paul winning the nomination is speculation.

When asked Wednesday if she could vote for Ron Paul, Rep. Michele Bachmann of Minnesota dodged the question by making that point: "He won't be the nominee," she said on Fox News. She added that he "would be dangerous as a president because of his foreign policy."

Rick Santorum said Wednesday he would "absolutely" vote for Paul if he were the Republican nominee, but said the idea makes him "nervous."

Research for this story didn't unearth direct comments on the issue by Texas Gov. Rick Perry or by former Utah Gov. Jon Huntsman Jr. As the other two Republicans seeking the nomination, they also differ with Paul on foreign policy.

In 2007, when endorsing Rudolph Giuliani for president, Governor Perry did say this, according to U.S. News & World Report: "We have to make choices in life, and I made a choice that Ron Paul's not mine for president.... I didn't have to study that too deep."