Why aren't the Republicans running?

[specific_name]

They don't think they can win?

The party was badly damaged at the end of the Bush era and that put them into something of an existential crisis. The 2010 primaries were one act of that crisis, where long time Republicans were being knocked off by insurgent radicals. It's created a fissure in the party, that reminds me of what happened to the Democrats before the last real realignment. That is the conservative Democrats split strongly from the progressives. Nixon then pursued the conservative Dixiecrats with his Southern strategy.

HHH's nomination temporarily kept the party together before it totally fell apart with McGovern, at least at the national level. History never repeats itself exactly, but these things are worth noting. The moderate Republicans were instrumental in nominating McCain, but the evangelicals, libertarians, paleo-cons and what would later be called Tea Parties were all left out in the cold. McCain is comparable to Humphrey if my analogy holds any weight.

Now if the Republicans try the opposite strategy and the mood shifts to an unelectable but "pure" candidate who generates enthusiasm from the base (somewhat like McGovern), we may see Obama in a Nixon like position. The president who is elected to end wars expands them and is attacked by the other party partially on those grounds. The candidate most likely to fill that position is someone like Bachmann. Unfortunately for the TP they don't have anyone sane and charismatic enough to get the nomination, so it looks like an establishment type will get it and lose narrowly.