TAMPA, Fla. — At the end of the Republican presidential debate in New Hampshire this month, when the Democrats joined the candidates on stage, Mitt Romney found himself momentarily alone as his counterparts mingled, looking around a bit stiffly for a companion.

The moment was emblematic of a broader reality that has helped shape the Republican contest and could take center stage again on Thursday at a debate in Florida. Within the small circle of contenders, Romney has become the most disliked.

With so much attention recently on the sniping between Sens. Hillary Rodham Clinton and Barack Obama on the Democratic side, the almost visceral scorn directed at Romney by his rivals has been overshadowed.

"Never get into a wrestling match with a pig," Sen. John McCain said in New Hampshire this month after reporters asked him about Romney. "You both get dirty, and the pig likes it."

Mike Huckabee's pugilistic campaign chairman, Ed Rollins, appeared to stop just short of threatening Romney with physical violence at one point.

"What I have to do is make sure that my anger with a guy like Romney, whose teeth I want to knock out, doesn't get in the way of my thought process," Rollins said.

Campaign insiders and outside strategists point to several factors driving the ill will, most notably, Romney's attacks on opponents in television commercials, the perception of him as an ideological panderer and resentment about his seemingly unlimited resources as others have struggle to raise cash.

Romney's campaign contends that the hostility is driven by how he has aggressively sought to win the early primaries, setting himself up as the chief antagonist, first, to Huckabee in Iowa and then to McCain in New Hampshire.

Romney continues to be a mountain in the paths of both men, as well as Rudolph W. Giuliani, to the nomination.

A spokesman for the Romney campaign, Kevin Madden, said, "I think it's largely driven by the fact that everybody's taught to tackle the guy on the field with the ball."

But the New Hampshire debate was striking in that it amounted to a gang tackle of Romney, even though McCain was leading in polls in the state.

"The glee the other candidates go after Romney with is really unique," said Dan Schnur, a Republican strategist who worked on McCain's presidential campaign bid in 2000 but currently is not affiliated with any campaign.

A senior adviser to Romney, Ronald C. Kaufman, pointed to his vast personal fortune and upstart status in politics as breeding resentment.

"They think he didn't pay his dues," said Kaufman, who argued that Romney had done so by working tirelessly in his campaign.

In stark contrast to Romney, McCain seems to be universally liked and respected by the other Republican contenders, even if they disagree with him.

Schnur used a schoolyard analogy to compare Romney, the ever proper Harvard Law School and Business School graduate, to McCain, the gregarious rebel who racked up demerits and friends at the Naval Academy.

"John McCain and his friends used to beat up Mitt Romney at recess," Schnur said.

Although McCain has now started to draw some cautious challenges from Giuliani in Florida, he has a long-standing friendship with him, dating from 1998, when they first met.

McCain also seems to have fallen into a mutual nonaggression pact with Huckabee, who has been almost fawning in his compliments for McCain and dripping with contempt when discussing Romney.

McCain has drawn criticism as being excessively personal in striking back at Romney. So he has tried to play down any notion that he harbors special animosity toward him, saying he simply does not know him well.

But McCain's advisers, whose distaste for Romney is vivid, say McCain has been irked by what they perceive as misleading attacks and Romney's willingness to say anything to be elected. "He doesn't play by the same rules the rest of us do," said Charlie Black, a senior McCain strategist.

McCain aides were positively gleeful last week as they watched replays aboard their campaign bus of a heated back and forth between Romney and an Associated Press reporter who challenged an assertion about the influence of lobbyists in his campaign,

Nevertheless, before he criticizes rivals, Romney often pauses to say that the man is a "friend" and he seems to believe it.

Giuliani endorsed Romney for Massachusetts governor in 2002 and campaigned for him. Romney got to know McCain while running the 2002 Winter Olympic Games and went to Washington to seek federal money.

Romney probably knows Huckabee the best, aides said, as the two were governors at the same time and ran into each other often through the Republican Governors Association and the National Governors Association.

Paradoxically, sometimes appears the enmity between them appears to be the sharpest. Aides to Huckabee say he did not get to know Romney very well as a governor, finding him distant at meetings. The aides said they were also irritated that Romney did not call after Huckabee's victory in Iowa.

Romney shrugged off any tension with his rivals when asked about it.

"You know," he said, "in this process, people have a real battle for success. But I consider these guys friends."

Contributing: Elisabeth Bumiller from Chicago