When you see a primary challenge against a long-time member of Congress, the incumbent usually enjoys the advantage of at least nominal support from the party establishment. It's pretty shocking to see Indiana Republicans abandoning Dick Lugar already:

Indiana state Treasurer Richard Mourdock will launch his primary challenge to Sen. Richard Lugar (R-Ind.) on Tuesday with the support of a majority of both the state's 92 Republican county chairmen and its state party executive committee, he told the Fix in a recent interview.
"I feel bad that he's going to be humiliated by this list," Mourdock said.
Mourdock added that he believes Gov. Mitch Daniels (R) and Rep.Mike Pence (R), the party's two leading figures in the Hoosier State, are going to stay neutral in the primary -- though Daniels, who was Lugar's campaign manager three different times, has already committed to voting for the senator. 

A couple points here. The challenge to Lugar, whose ideological apostasies are quite limited, is yet another step in the ideological remaking of the Republican Party. The GOP is moving right at a breathtaking pace, and primary challenges like this are accelerating the pace of change. They have the direct effect of replacing moderate or moderate-esque members of Congress with more conservative ones. They also have the indirect effect of persuading other Republicans to stay in line lest they find themselves challenged as well. The trade-off is that the party has to accept a greater chance of losing -- Lugar is a sure-fire winner, whereas Mourduck would run at least some chance of losing -- in order to attain this greater ideological cohesiveness.

But it's a tradeoff the party has shown itself willing to accept over and over. Keep in mind, the Senate is structurally tilted toward Republicans. Small-population states, which have disproportionate representation, are disproportionately Republican. In 2000, George W. Bush won 30 states despite losing the popular vote. Republicans don't need to win Democratic-leaning states in order to control the Senate. They can gamble on more conservative candidates.

Finally, Lugar looks like a dead man walking to me, at least as a Republican. If I were him, I'd be carving out an independent profile and looking to run a third-party campaign in 2012. That's his best chance of holding a Senate seat.