After Republicans reclaimed their majority status in the House in the 2010 election, many pundits predicted the party would have an easy time capturing the Senate in 2012. There are, after all, only 10 GOP senators up for reelection, compared to 23 Democrats. And Republicans seemed to be successfully riding a wave of anti-government sentiment to victory against an embattled president.

But as one political showdown after another has illustrated just how beholden congressional Republicans are to extreme right-wing interests, their prospects for retaking both chambers have grown dimmer.

Republican Sen. Dick Lugar (IN) recently reinforced that sentiment in an interview with CNN, explaining that the Tea Pary’s insidious influence has pushed out moderate elements of the party...