Jonathan Martin reports that Mitt Romney has not re-upped his television ad buys in South Carolina, suggesting that Michigan will make or break his campaign. Michigan is an open primary. Independents and Democrats can vote in the GOP contest. And since the Democratic primary is uncontested, more than a few - though probably not many - Democrats may cast a vote for a Republican. An open primary favors John McCain. Meanwhile, Mike Huckabee has gone on the air in Michigan and plans to emphasize his populist themes in a speech at the Detroit Economic Club later this week. Huckabee came in a surprise third in New Hampshire. What if he comes in second to McCain in Michigan? Regardless of whether or not that happens, Romney's campaign is over if he loses in Michigan. Which means there would be four candidates - McCain, Huckabee (now the national frontrunner), Giuliani, and Thompson - competing in South Carolina. Thompson hasn't done much, and barring a surprise outcome in South Carolina, it's likely he will depart the field after the Palmetto state votes and rejects him. That would leave three candidates - McCain, Huckabee, and Giuliani - to compete in Florida. The GOP race may go from a five-way to a three-way in a little more than a week from now. And then comes the interesting part. A lot of conservatives have problems with both Huckabee and McCain. Last night on Fox, for example, Sean Hannity could barely conceal his distaste for both pols. Rush Limbaugh and the Wall Street Journal editorial page also have problems with the Huck and the Mac. National Review endorsed Romney in December. How would these conservatives cope with Romney's failure? It's possible they will side with McCain in the end. Some of them may give Giuliani a second look. But a disappointing finish for Rudy in Florida would make this a two-man race by late night January 29 . Then Republicans would choose between the preacher and the warrior. Of course, the way things have been going so far, it's likely we'll be blindsided a few more times before the race is won.