This is based off historical patters based off Republican wins in the past.
I think the only way that this pattern can be broken is if the Tea Party really vets the best candidate possible that could and would implement what is needed to bring this Federal Government under control. If that does not happen, the Republican Party would most likely nominate Mitt Romney, as the next candidate, here is why I think that.
Based on historical trends, the number two candidate of the previous election cycle normally becomes the number one contender for the Republican Party.
2008: John McCain, he was the number two contender in 2000.
2000: George W. Bush became the number one contender due to his name recognition.
1988: George H. W. Bush, was the number two contender in 1980, when Ronald Reagan won. Due to him being the sitting Vice President and name recognition he became the number one contender and won the presidency.
1980: Ronald Reagan won, after he ran in 1976 against Gerald R. Ford, and lost the nominee, but he was the number two contender.
1968: Richard Nixon won the Presidency, after running against and losing to John F. Kennedy in 1960.
If this trend holds up, Mitt Romney should be the number one Republican Contender against Barack Obama in 2012. He came in at number two against John McCain in 2008. After the election, many conservative pundits lamented not backing him up during the 2008 election, many believing, as do I, that he could have been the only Republican to defeat Barack Obama.
Unless there is some kind of unforeseeable event, or a more popular or more name recognized contender enters into the election, look for Mitt Romney being the number one contender for the Republican Party in 2012. The only person I could see that could unseat Mitt Romney would be Jeb Bush, but presently, I do not see him putting his hat into the race at this time. Many do see Jeb Bush as a possible contender in the near future, maybe 2020?