Until now the two Republican presidential candidates have been convenient allies - the two David's who knocked down Mitt Romney, the financial Goliath. But there's nothing convenient about Michigan and South Carolina, states that could make or break either candidate's hopes for being the next Republican presidential nominee.
So these two men who separately confronted Romney, one in Iowa and one in New Hampshire, are now in the same ring.
"I don't see us going out there and taking the gloves off," Huckabee said of the prospects of a tough encounter with McCain.
To be sure, McCain and Huckabee appeal to separate wings of the Republican Party. Iowa with its greater share of social conservatives and evangelicals was better suited to Huckabee. New Hampshire, with its independents and national security minded voters, preferred McCain.
Who wins depends on who else they can draw in with their distinct messages - McCain's national security savvy and independent streak or the former Arkansas governor's religion-streaked economic populism.
The two tend to like each other - Huckabee has called McCain a "genuine American hero." So far neither shows any inclination to go after the other with the same zeal with which Romney went after both of them.
But neither of them is reluctant to pull his punches if confronted. McCain did it directly, airing ads in New Hampshire quoting newspapers that called Romney a phony. And Huckabee prepared a negative ad against Romney in Iowa, chose not to air it, but showed it to the media anyway.
Huckabee campaign manager Chip Saltsman, speaking to reporters the night of the Iowa caucuses, conceded as much: "It's politics, and it may get a little rough."
The first inkling could come as soon as Thursday, when the Republican candidates gather in Myrtle Beach for a debate.
Flying in to South Carolina from his third place finish in New Hampshire, Huckabee on Wednesday hinted at the contrasts he might draw with McCain. His main argument: He is a governor with executive experience, McCain is a U.S. senator with armed services expertise.
"The idea that he's had longer experience, ask Joe Biden and Chris Dodd what it did for them," he said of two Democratic senators who bowed out of the presidential race. "There are not two more experienced people in terms of foreign policy and military background than Chris Dodd and Joe Biden. But they took one, two percent, something like that?"
Ed Rollins, a senior adviser, put it succinctly: "A governor makes decisions. A senator doesn't make decisions; a senator sits and listens and learns and casts votes."
McCain is looking to repeat his 2000 victory in Michigan, eager to court independent voters in the state. Romney is putting all his resources in Michigan and hoping that his role as native son and fond memories of his father, who was governor there, will boost him to victory. Huckabee could be a spoiler, tapping religious, social conservatives in the state's rural regions and among economically anxious workers closer to the manufacturing centers.
In South Carolina, Huckabee is leading in the polls and it there that the contest with McCain is likely to be head-on. Huckabee is already exploiting an issue that could be damaging to McCain - immigration - by running ads in the state promoting his tougher proposal for treating illegal immigrants.
Still, Romney remains a factor. Following his second place finish in New Hampshire, Romney pulled his ads from Florida and South Carolina, where he had invested heavily, to focus his finances on Michigan. A victory in Michigan for Romney would send him back to South Carolina with new life.
That would complicate things for Huckabee. Romney would be competing for some of his same voters, opening a path for McCain to win.
But Huckabee has quickly built his lead in the state, becoming a favorite with religious and working class voters.
His traveling bus bears an enormous likeness of him and a the logo: "Faith, family, freedom." And his speeches Wednesday were laden with religious and anti-abortion references that were not as prominent when he stumped in New Hampshire.
"If we were to say that the taking of an innocent life is not wrong, then nothing is wrong," he told a rally in Spartanburg, before visiting a church-assisted pregnancy center that attempts to persuade women not to have abortions.
It is common at Huckabee events to find parents with their home schooled children, many of them devout Christians.
"Mothers and fathers raise better kids than governments do," Huckabee says.
But Huckabee is aiming for a swath of voters beyond the religious and opponents of abortion. His government-off-our-backs, end-the-income-tax proclamations could resonate with young, working class people.
"South Carolina is just a state designed for a guy like Huckabee," said Clemson University political scientist David Woodard. "If he can pull a surprise in Michigan, and comes in with a full wind, he could level the field."