Richard Lugar faces challenge

Larison covers the challenge from Indiana's State Treasurer, Richard Mourdock:

There is some merit to the charge that Lugar has moved left in recent years. Lugar’s lifetime ACU rating is 77, which isn’t terrible, but it’s a lot lower than one would expect from a Republican member of Congress in Indiana. By comparison, the ousted Utah incumbent Sen. Bob Bennett had a lifetime rating of 83. Even after we take into account that the ACU scored Lugar’s support for New START as a negative, his rating for the last two years has been below that lifetime rating.
One thing I would recommend to Mourdock is that he stop trying to pretend that he understands arms control better than Lugar. He doesn’t. It has never made sense to me why so many Republicans want to make opposition to this treaty into a litmus test, but it makes absolutely no sense to try to make Lugar’s support for the treaty into a significant issue in the primary. This is one of Lugar’s specialties, and it’s something that he takes very seriously. Lugar will be able to bat down Mourdock’s rehashed distortions without even trying, and by trying to demagogue on arms control Mourdock will simply expose himself to ridicule. Mourdock will only weaken his case for nomination if he tries to go up against Lugar on one of his strengths.

I don't understand the Republican opposition to the new START treaty.  I also don't understand the Republican test for ideological purity in all votes.  I agree with Daniel that it is healthy for somebody to challenge a politician who has been in Congress for 35 years, but I would like to see the GOP stop the swing to the right.  We need some grown-ups in our government, not a bunch of ideologues.  I've respected Richard Lugar over the years, much like I thought of George Voinovich.  I think the Republicans need more politicians like them, not less.  Unfortunately, the GOP base and I see things much differently, that's why I left the party.