Indianapolis, Indiana (CNN) -- Richard Lugar's landslide loss in Tuesday's Indiana Republican primary isn't just a 36-year veteran getting tossed out of office before he wanted to go.
It's also the latest blow to the political center in an increasingly polarized Senate.
Already, nearly half a dozen moderate senators in both parties are retiring this year.
Some, such as Republican Olympia Snowe of Maine, made clear in her surprise announcement earlier this year she's leaving because she can no longer stand the partisanship and inability to get things done.
Two years ago, several centrist Republicans were toppled by tea party-backed candidates.
In the case of Lugar, his opponent, Richard Mourdock, argued successfully to Indiana GOP voters that Lugar, a moderate, too often supported President Barack Obama's agenda.
Mourdock, who won with support from tea party-aligned groups from around the country, advocates confrontation over compromise.
"What I've said is, and what I continue to believe, certainly, is one side or the other must prevail, and I'm hoping this candidacy will help move the Republican Party forward to become a permanent majority," Mourdock told CNN on Election Day.
In the face of his defeat, Lugar told CNN that "people don't understand the legislative process." To get things done, he said, you have to compromise.
"Some people say, well, we do understand it, and by golly, we're going to wait until we have majorities in both houses, the White House, where there's two years, four years, six years, but the country has to keep going in the meanwhile," Lugar said.
As Lugar left his election night headquarters after giving his concession speech, the 80-year-old senator instructed campaign aides to distribute a statement that was quite extraordinary in the annals of politics.
It was partly a detailed defense of his ill-fated and often maligned campaign strategy and partly a stark warning to both parties about the divisive state of American politics, starting with Mourdock.
"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. In effect, what he has promised in this campaign is reflexive votes for a rejectionist orthodoxy and rigid opposition to the actions and proposals of the other party," Lugar wrote.
He also said if Republicans continue to make it difficult for legislators to find compromise, "we will be relegated to minority status. Parties don't succeed for long if they stop appealing to voters who may disagree with them on some issues."
But U.S. Sen. Ron Johnson of Wisconsin, a Republican swept into office on the tea party wave two years ago, suggested Lugar's harsh words for many in his party were mostly about his own personal loss.
"These elections are tough battles, and people probably have hard feelings when they don't win. But the fact of the matter is that people like me -- and I think also people like Richard Mourdock, people that actually had tea party support -- we love this country. We are so concerned about the fact that we are burdening our children, grandchildren with debt that is simply unsustainable," Johnson told CNN.
Though most senators willing to cross party lines are either gone, or in the case of Sen. Orrin Hatch, moved enough toward the base of their party to stay alive, there are a few exceptions.
Scott Brown is one. To win in Democratic Massachusetts, the Republican plays up crossing party lines, in this new ad called "Independent."
It features a clip from CBS's "60 Minutes" describing Brown as "unpredictably independent, and beholden to no one."
The problem for Lugar is he tried that in his Republican primary in the red state of Indiana.
It may have worked in times gone by, but in 2012 politics, his argument that he reaches across the aisle was a negative for Lugar, something he lamented in the face of his landslide loss.
"We have been a factor in pulling people together so we reach decisions. The public as a whole may be unhappy with one party or the other, but they're very unhappy with the Congress as a whole for their inability to make decisions," Lugar said.
CNN's Deirdre Walsh contributed to this report.