Far from politics, six-term Sen. Richard Lugar is considered a visionary who looked beyond U.S. exuberance over the end of the Cold War and saw the dangers and opportunities in the collapse of a nuclear-armed Soviet Union.

In an age that worships whiz kids from Wall Street to Silicon Valley, the 80-year-old, soft-spoken Republican is widely described as a man ahead of his times, a thoughtful leader in the international arena who valued cooperation over partisanship. In 1991, he collaborated with former Democratic Sen. Sam Nunn on landmark legislation to help the former Soviet states destroy and secure their weapons of mass destruction, a program still going full bore today with thousands of nuclear warheads eliminated and nearly a thousand long-range missiles destroyed.

That singular achievement in a 35-year Senate career focused heavily on foreign policy and national security made Lugar's decisive defeat in Tuesday's Indiana primary so painful for Republicans and Democrats alike.

"I'm just devastated," Sen. Susan Collins, R-Maine, said in an interview Wednesday. "He is such a fine person and has made so many contributions to this country's security and to the security of the entire world through the work he's done on nuclear non-proliferation. I just can't imagine the U.S. Senate without Dick Lugar, so I'll miss him terribly."

Nunn, the former chairman of the Armed Services Committee, described a working relationship that seems rare in contemporary Washington.

"We developed a sense of trust, and we developed a sense of cooperation," Nunn said in an interview. "Trust in politics is misunderstood today. Some take it as meaning you compromised your principles. Dick Lugar never compromised his principles in anything we did together, nor did I. We found ways to work together because we examined the facts and let the facts have a bearing on the conclusions, and I'm afraid in today's political world too often people start with the conclusions and then hunt facts to justify them."

Lugar's loss was a blow to the diminishing center of the Senate that has searched for compromise. Moderate Sen. Olympia Snowe, R-Maine, stunned her party earlier this year when she announced she wouldn't seek another term. At least a handful of moderate Democrats and one independent won't be back next year — Kent Conrad of North Dakota, Ben Nelson of Nebraska, Jim Webb of Virginia and Joe Lieberman of Connecticut. All opted for retirement.

Two other moderate Democrats — Claire McCaskill of Missouri and Jon Tester of Montana — are the most vulnerable this election cycle.

One of the most telling developments occurred last September after the bitter fight over spending and the debt. Sen. Lamar Alexander, R-Tenn., quit the leadership for his independence and the opportunity to help fashion bipartisan solutions.

Sen. Bill Nelson, D-Fla., who faces a tough challenge in his re-election bid, bemoaned "an intolerance that is creeping into our politics that I think is very destructive and we're seeing a lot of that in this ideological rigidity and this excessive partisanship."

Indiana state treasurer Richard Mourdock, who easily beat Lugar, is unapologetic in his scorn for compromise. He simply wants to beat the other side, an approach Lugar dismissed in his concession speech as ineffective.

"He has pledged his support to groups whose prime mission is to cleanse the Republican Party of those who stray from orthodoxy as they see it," Lugar said Tuesday night. "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."

Collins insisted she will continue to work from the center to reach consensus with Republicans and Democrats. Defiant partisans ignore a political reality, she said.

"I think that no one in this chamber should forget that our approval rating is 13 percent," she said. "So the American people are not happy with the polarization."

Lugar, a conservative, was tripped up in his campaign by his willingness to compromise, questions about his residency in Indiana and his longevity in office. He was elected in 1976, the year Jimmy Carter came to Washington. The top Republican on the Senate Foreign Relations Committee, Lugar built a career in national security, issues that lack the imperative of jobs in a sluggish economic recovery.

"He's achieved many things in the foreign policy arena," said Sen. Dan Coats, R-Ind. "That's one of the essential roles of the Senate. But that's not what's on people's minds today during this time of tough economic times. People are just discounting that."

Mourdock won handily, 60-40 percent.

In a speech on the Senate floor Wednesday, Foreign Relations Committee Chairman John Kerry, D-Mass., said Lugar "refused to allow this march to an orthodoxy about ideology and partisan politics to get in the way of what he thought was the responsibility of a senator and ... the need of the country to have people come together and find the common ground."

Sen. Dick Durbin, D-Ill., said of Lugar's defeat: "It's a sad day on both sides of the aisle."

During his tenure, Lugar has been the point man for presidents on arms control treaties, steering strategic arms reduction pacts to reality for Presidents George H.W. Bush, Bill Clinton and Barack Obama. He backed NATO expansion, insisted that the United States pay its dues to the United Nations and favored aid to the Nicaraguan Contra rebels as he headed the Senate Foreign Relations Committee from 1985-87 and 2003-07.

He ran for president in 1996 on a slogan of "nuclear security and fiscal sanity." It was Lugar, as mayor of Indianapolis in the late 1960s, who steered the city financially and argued against federal programs. That earned him the title of President Richard Nixon's favorite mayor.

In August 2005, Lugar and the new senator from Illinois, Barack Obama, traveled to Russia, Ukraine and Azerbaijan to check on the progress of nuclear disarmament. That earned Lugar the title of Obama's favorite Republican, a moniker used against him in the campaign.

In a statement Tuesday, Obama praised Lugar as a man who "comes from a tradition of strong, bipartisan leadership on national security that helped us prevail in the Cold War and sustain American leadership ever since."

Earlier this month, Lugar released the latest scorecard from the Nunn-Lugar cooperative threat reduction program established to help the former Soviet states destroy nuclear, chemical and biological weapons and safeguard the remaining material to keep it from the hands of terrorists. To date, 7,619 strategic nuclear warheads have been deactivated, 902 intercontinental ballistic missiles destroyed, 498 ICBM silos eliminated, 155 bombers destroyed and the list goes on. Ukraine, Kazakhstan and Belarus are nuclear weapon free.

"Richard Lugar's a national hero," said Joe Cirincione, president of the Ploughshares Fund, a group dedicated to disarmament. "If he wasn't there, we would face greater threats today. We're safer because of what he's done."

Lugar's loss, said Cirincione, "does more to weaken our national security than dozen of terrorists threats in the Middle East."