The hit men of the tea party can carve another notch in their collective gun belts this week with the ouster of Indiana Sen. Richard G. Lugar, a 35-year veteran of the U.S. Senate. Whatever mojo the conservative firebrands had in the 2010 GOP primaries, when they ousted party moderates right and left, is apparently still working for them.

Longtime incumbents are not easily toppled, but Mr. Lugar's vulnerabilities were well-documented prior to Tuesday's Indiana primary: The six-term senator is 80 years old, has lived in Northern Virginia for decades (despite using a 1970s-era address for voting purposes) and seemed to voters far more interested in foreign policy than in the daily concerns of the folks back home.

Nor did it help that Mr. Lugar, ever the Midwestern gentleman, didn't go after his opponent, state Treasurer Richard E. Mourdock, with the same vigor the challenger demonstrated against him. Conservative groups spent millions of dollars to support Mr. Mourdock, who expresses a clear preference for confrontation over compromise with Democrats.

So while Mr. Lugar is an imperfect poster child for the death of Republican moderation, his defeat still echoes the sad reality of U.S. politics in the second decade of the 21st century: The gulf between Republican and Democrat, conservative and moderate (let alone progressive) has never been greater in living memory.

What was Mr. Lugar's crime that sparked such disdain? It was those occasional moments when he showed a willingness to find common ground with the other party. Even his votes in support of President Barack Obama's Supreme Court nominees were treated as treasonous. In contrast, Mr. Mourdock claims the only way forward is for the GOP to seize total control and never give ground to the other party. He is best remembered beyond Indiana's borders for vigorously opposing President Obama's auto industry bailout, despite the thousands of jobs it saved in his state.

In conceding defeat, Mr. Lugar urged Mr. Mourdock, if ultimately elected to the Senate, to reconsider his promise of bringing even greater partisanship to Congress. "He and I share many positions, but his embrace of an unrelenting partisan mindset is irreconcilable with my philosophy of governance and my experience of what brings results for Hoosiers in the Senate."

Indiana, which advertises itself as the "Crossroads of America," may now reflect a political crossroads, of sorts, in a hopelessly divided country. Mr. Lugar is not the only pragmatic Hoosier to struggle with the polarization that has descended on the nation's political scene.

Two years ago, Sen. Evan Bayh, a two-term Democratic moderate and former governor, announced he would not run for re-election because of the "brain-dead partisanship" that had infected Congress. His seat is now occupied by Sen. Dan Coats who, in an earlier term in the Senate, once questioned the timing of President Bill Clinton's attack on terrorist bases in Afghanistan and Sudan in 1998 as potentially linked to the Monica Lewinsky scandal.

Mr. Lugar's departure is not just some changing of the guard or passing of an old lion of the Senate, but one more straw on the camel's back of sensible decision-making. The Senate, in particular, needs members of both parties to work together given that it's highly unlikely either party will muster a 60-vote, filibuster-proof majority next term.

Yet it will have to accomplish this without the handful of centrists who will be leaving after the November elections, including Democrat Jim Webb of Virginia and RepublicanOlympia J. Snowe of Maine. Any hope for a do-something Congress would seem slight, at best, no matter whom we elect president.

To paraphrase Mr. Lugar, voters may hate the policies of one party or the other, but they hate even more when Congress is unable to make decisions. Perhaps the next Congress will rise to the challenge when push comes to shove and inaction gives rise to genuine crises. But it's far more likely that the insights of a six-term senator will have fallen on deaf ears, and the next term will bring more of the same partisan paralysis.