On Tuesday, Indiana Republicans voted to end the Senate career of six-term incumbent Richard Lugar in favor of Richard Mourdock, a tea party conservative.

Mourdock is probably best-known outside his home state for his quixotic and losing fight against the Chrysler bailout. His objections were based on the idea that the bailout helped the United Auto Workers Union more than Chrysler's stockholders.

Lugar is a conservative. The American Conservative Union at one time rated his voting record as 90 pecent, but over time, as the Republicans moved further right, it fell to the 70 percent range.

His legislative accomplishments include the Nunn-Lugar act, which tightened control of nuclear materials, and without which it would be easier for terrorists to obtain fissile materials.

More recently, Lugar also introduced the Good Samaritan Hunger Relief Act of 2011, which gives tax credits to farmers and small businesses that contribute food products to food banks and homeless shelters. He has long been a champion for what he calls "global food security." Both of these bills were bipartisan, and if "compassionate" conservatism ever had a face, it would have been Lugar's.

His politics were informed by Midwestern conservatism, but they were also shaped by pragmatics. He knew the importance of reaching consensus, and by dealing with members of the opposition party, he got more accomplished than the extremists on either side of the political spectrum ever could. On the other hand, he was willing to play partisan political hardball, voting against raising the debt ceiling and for a balanced-budget amendment.

Four factors contributed to Lugar's defeat. First, the general anti-incumbent attitude of many voters didn't help his chances. Second, Lugar is 80 years old, and his opponent turned both his age and incumbency into election issues. Third, primary election voters tend to be more partisan than the population at large, and finally, Mourdock hammered at Lugar's conservative bona fides. The very same principles that made Lugar an effective senator, his willingness to seek common ground with Democrats, became a weapon to be used against him by a younger, more zealous (and less principled) ideological purist.

Two certain consequences of Lugar's defeat are the continued radicalization of the Republican Party and putting an otherwise safe Republican seat in play for 2012. This year, Republican moderates have either been drummed out of office, as happened to Lugar, or like Olympia Snowe, got fed up with the immoderate conservative wing's intransigence and inflexibility.

The right-wing purge of moderates began years ago, but it didn't build up momentum until moderates like Jim Jeffords, Lincoln Chafee, Lisa Murkowski, and Lowell Weicker either left the party or, like Lugar, lost primary elections to extreme conservatives. Later, we will discover whether a more conservative, but still consensus-seeking incumbent, Orrin Hatch of Utah, can defend his seat from another tea party conservative.

After his defeat, Lugar ripped into Mourdock, saying that he embraced "groups whose prime mission is to cleanse the Republican Party of those who stray from orthodoxy as they see it." He went on to say, "This is not conducive to problem solving and governance. And he will find that unless he modifies his approach, he will achieve little as a legislator. Worse, he will help delay solutions that are totally beyond the capacity of partisan majorities to achieve."

This drive toward ideological purity cannot be good for Republicans or the country. If anything, a political party needs to broaden its base, not shrink it. In 1964 the Republicans turned to Barry Goldwater. In 1972, the Democrats chose George McGovern; in both cases, the country massively rejected these far-from-the-center candidates. In 2012, the right wing pushed Mitt Romney very far away from the center in the name of "severe conservatism." Republicans may very well come to regret this purge and the hardened feelings they have created among moderates.