It WILL be Romney
Rick Perry's propensity for gaffes, poor straw poll performance, and lackluster debating skills are already forcing many people who thought he would surely be the Republican nominee to reconsider. They're right to have second thoughts, yet while Michele Bachmann, Herman Cain, and even Jon Huntsman may go on to win some primaries, none have a real chance of becoming the nominee either.
This leaves only one person standing: Mitt Romney. Whatever ups and downs take place for the Romney and Perry campaigns, it's pretty obvious what will happen: Romney will prevail.
The Republican nominating process, quite simply, gives a massive advantage to those who have "been around the block" before. Since end of the Eisenhower administration, all but two people to emerge as the winner from the Republican primary process--Barry Goldwater and George W. Bush--were, in some sense the "runner up" in a previous presidential nominating process. (In 1968, Nixon was previously an unsuccessful nominee.) George W. Bush, furthermore, almost certainly outperformed in early polls because people thought he was his father. And, in any case, he could also tap his family's vast political network.
And networks like this one are what really decides the Republican nominee. Republican primary voters hold all of the weight in the process. There are no Republican super-delegates and Republican primary voters (not without reason) do not believe that media sources give their candidates a fair shake. Support from county party chairs, Republican clubs, and conservative activist groups matters a lot more than fund raising or even gross support in the polls.
Nobody can build this type of support overnight: getting it often requires the physical presence of the candidate. Mitt Romney has had six years to visit with the people who really decide on the Republican nomination. Neither Rick Perry nor anyone else can duplicate his efforts in six weeks.