Dick Lugar was defeated in a primary by that fool Murdock. Dick Lugar is one of the most serious foreign policy voices in the United States Senate. He got freaking primary'd by the tea party. The people that used to vote Republican are being shoved by a committed group of 25-30% of the electorate that forces Republicans to bow down or gtfo. There are absolutely interest group politics on the left, but it has become such a diverse set of interests that it has mostly woven itself in to the generally electorate. Meanwhile, demographics and fundamentalism is going to doom the Republicans.
But look, let's not get out of hand. It is hard to beat an incumbent.
Bush I
Clinton
Clinton
Bush II
Bush II
Obama
Obama
Republicans will have an excellent shot in four years. Anyone that pretends to know what their candidate will be or what the Democratic nominee will be is nuts. But a lot of issues on the ground are going to make fools of the religious right. Gay Marriage, Pot, Birth Control, Immigration. These are devastating losers for the right long term.