“It’s clear the negative ads are what’s keeping this guy alive”

As successful as the strategy has been, though, it has raised questions about Mr. Romney’s role in turning the primary process into something akin to a civil war, even as it has demonstrated a ferocious, whatever-it-takes style that could hearten Republicans if Mr. Romney ends up in a general election matchup against Mr. Obama.

“It’s clear the negative ads are what’s keeping this guy alive,” said Nelson Warfield, a Republican strategist who worked for Mr. Perry. “It seems like Republican primary voters will not vote for Mitt Romney unless they are forced into it. And the way they’re forced into it is when he beats the other guy senseless.”…

Mr. Romney’s rivals have long feared the ability of his formidable message machine to tear opponents down. But they are also consoled, they said, by the fact that his campaigns have often struggled to create a positive image for him.

“I think that’s Romney’s M.O. His success in politics has come by running tough, hard, negative campaigns against opponents,” said Tad Devine, who helped run Mr. Kennedy’s campaign against Mr. Romney. “And the thing about negative campaigns, and I have certainly seen this up close and from afar, is they come at a cost. When you spend most of your political capital doing that, it leaves you open.”