The U.S. Senate is losing its longest-serving Republican and a senior statesman. Senator Richard Lugar of Indiana lost a primary election to fellow Republican Richard Mourdock, who was backed by the conservative Tea Party movement. For more than three decades, Lugar helped forge bipartisan consensus on critical foreign policy matters, most notably nuclear arms control.

A globetrotter who left his mark in Europe, Asia and beyond, Richard Lugar expressed no regrets over his Senate career, which will end in January.

"I am proud of the solutions we have brought to problems over the years and the initiatives we have undertaken to build Indiana and to protect our country," Lugar said.

A six-term senator and the top Republican on the Senate Foreign Relations Committee, Lugar is best-known for co-sponsoring a 1991 program that helped former Soviet states eliminate thousands of nuclear weapons.

"That was the beginning of what has led to the dismantling of well over 60 percent of the warheads literally taken off the missiles pointed at the United States, the destruction of well over 60 percent of all the missiles, of the silos in which the missiles are based, of all the ground work," Lugar said.

Cngressional observer Thomas Mann says Lugar's departure will leave a void in the Senate.

"They are losing a respected foreign policy leader, and they are losing someone who is not instinctively engaged in tribal politics between the parties," Mann said.

Although a staunch conservative, Lugar did not shy from criticizing the former Bush administration over its response to the 2001 terrorist attacks.

"We are worried about terrorism, but the evolution of national security policy has not kept up with the threat. We have relied heavily on military options and unilateral approaches that weakened our alliances," Lugar said.

Lugar lost a primary election Tuesday, which means he can not run as the Republican candidate in November. His opponent, Richard Mourdock, portrayed him as a member of Washington's political establishment and attacked Lugar's willingness to seek common ground with Democrats.

A day after Lugar's defeat, Democratic senators paid tribute to him as a consensus-builder in an institution increasingly paralyzed by partisanship. Foreign Relations Committee Chairman John Kerry:

"He was serious, he was thoughtful, and he 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, indeed, the need of the country to have people come together and find common ground," Kerry said.

Lugar says he hopes to remain engaged in world affairs and to continue to serve the nation.