At the Fox News Forum two days before the New Hampshire primary, when McCain was locked in a tight race with Romney, Huckabee, who was trailing both, went after Romney right out of the gate.
Incidents like these have led to speculation about a McCain-Huckabee mutual assistance pact.
Jill Hazelbaker, McCain's communications director, says there is no such political arrangement, just a genuine friendship.
"It's sincere, not some sort of 'alliance' as the media suggests at times," she said in an e-mail. "He [McCain] likes him very much and admires his talents."
McCain often asserts that attack-style campaigning is distasteful and, as a practical matter, that it runs the risk of backfiring by turning off voters. When Romney and former New York City Mayor Rudolph Giuliani were blasting Sen. Hillary Clinton, D-N.Y., in the fall, McCain laid off, refusing to "degrade or ridicule" her.
According to recent polls, McCain holds a modest lead over Huckabee in South Carolina. With so much at stake, both men may be tempted to heat up the rhetoric or even go negative on the airwaves.
As Newsweek put it: "Will the mutual back-scratching end and the attack ads begin? Will McCain and Huckabee become the very thing they profess to abhor while savaging each other? Once victory and power seem possible, there is a temptation to pick up the old cudgels of politics."
McCain vows that won't happen.