WASHINGTON -- For over a decade, the bipartisan trio of senators traveled the world together, from war-torn Iraq to Germany for security conferences to the remote kingdom of Bhutan. Their hawkish world views often placed them at odds with their respective parties, but together they secured a place at the center of every major foreign policy debate.
Now the senators -- John McCain of Arizona, Joseph I. Lieberman of Connecticut and Lindsey Graham of South Carolina -- a triumvirate of frequent fliers dubbed "the three amigos" by David H. Petraeus, then a general -- are breaking up the band, as Mr. Lieberman retires in January. For Mr. McCain and Mr. Graham, the loss of Mr. Lieberman, a Democrat turned independent who is chairman of the homeland security committee, goes beyond personal deprivation, and could profoundly affect their ability to influence foreign policy. Though he frustrated many Democrats with his interventionist ideas, Mr. Lieberman gave Mr. McCain and Mr. Graham the veneer of bipartisanship that lent credibility to their policy goals.
An illustration of life without Mr. Lieberman surfaced recently when Mr. McCain and Mr. Graham, along with a new amiga, Senator Kelly Ayotte, a Republican freshman from New Hampshire, broke with Mr. Lieberman and most other senators by calling for a special committee to investigate the deadly attack in Benghazi, Libya. The push quickly fell flat and Mr. McCain, who had harshly criticized Susan E. Rice, the ambassador to the United Nations, over the September attack, this weekend appeared to retreat from his original assertion that Ms. Rice was unqualified to be secretary of state.
"I think she deserves the ability and the opportunity to explain herself and her position," he said on "Fox News Sunday," adding, "she's not the problem." The question is whether the group, whose profile rose in the wake of the Sept. 11, 2001, attacks, will be able to maintain an influential voice without Mr. Lieberman, or become isolated on an island of partisan poking.
"I think it's becoming increasingly difficult for them to defend their positions," said Senator Richard J. Durbin of Illinois, a member of the Senate Foreign Relations Committee and the No. 2 Democrat in the Senate.
Even Mr. Lieberman seemed skeptical of a one-party band. "I think John McCain and Lindsay Graham will always be leaders on foreign policy," he said in an interview. "But their voices would be stronger if they are part of a bipartisan group."
Mr. Lieberman and Mr. McCain became friendly in the late 1980s, when both men joined the Senate. "I approached John on the floor and said, 'Hey I'd like to work with you on some things,' " Mr. Lieberman said. The two were united on issues like the war in Bosnia and efforts to stabilize post-Soviet republics. Their travels began with an annual security conference in Munich, and they added other venues.
"We felt if you're going to take a position on what is happening in the Balkans or Asia," Mr. Lieberman said of their dozens of trips, "you better go there and meet and talk to people."
When Mr. Graham was elected to the Senate in 2002 he joined the duo, whose militaristic foreign policy views suddenly had deeper resonance. "The 'amigo' dynamic really began to materialize after 9/11," Mr. Graham said in an interview. "Everything changed about American security threats then." (Mr. McCain declined to be interviewed.)
The three men became even more powerful in 2007 as President George W. Bush pursued his "surge" strategy in Iraq. The Republicans had just lost the House and the Senate, in no small part because of the Iraq war, and both parties were highly skeptical of the president's decision to double down on troops levels in Iraq under General Petraeus. Mr. Lieberman's pressure on the Senate floor day after day helped prevent the earlier withdrawal sought by many Democrats.
"Our biggest contribution was giving the surge a chance and giving Bush political cover to change strategies," Mr. Graham said. "Joe was the real hero because he denied the Democrats the 60th vote to set a timeline for withdrawal. If that had not happened, we would have never had the surge."
The success of the operation earned them further respect among their colleagues, even though the overall wisdom of entering the war is something many members who voted to authorize it say they regret. "I have no regrets about taking out Saddam," Mr. Graham said. "But I have a lot of regrets that we didn't understand what we were getting into better."
The three did not agree on every military issue. Mr. Lieberman broke with the others on various policies, most famously when he became a vocal opponent of the Clinton-era don't ask, don't tell policy governing gays in the military. He and Senator Susan Collins, Republican of Maine, successfully pursued its repeal.
While other senators, including Republicans, have been tossed from Mr. McCain's inner circle for disagreeing with him so publicly, Mr. Lieberman remained firmly in his camp, perhaps the only member who enjoyed such immunity from Mr. McCain's well-documented temper.
"We're really a band of brothers," an emotional Mr. Lieberman said of their relationship. "What is perhaps important about that is that in a time of increasing partisanship and ideological rigidity, that friendship has transcended the obvious differences between us."
After Mr. Obama's first years in office, the trio seemed to lose some of its power on foreign policy issues, and often appeared to be scolding the Obama administration rather than seeking bipartisan policy solutions. The foreign policy landscape is / especially complex now that there are so many intraparty differences in the wake of the Arab Spring.
"There is so much more of a muddle on foreign policy now," said Jon B. Alterman, the director of the Middle East Program at the Center for Strategic and International Studies. "I testified before the Senate Foreign Relations Committee in April on Syria, and I couldn't understand what the partisan line was." Some lawmakers have argued for deeper sanctions or more assistance to the Syrian opposition, while others are against both notions, but not along party lines.
That dynamic makes notable the inclusion of Ms. Ayotte, a member of the more conservative wing of Senate Republicans, who has traveled with both Mr. McCain and Mr. Graham.
Ms. Ayotte said she began working with the pair on the issue of detainees. Of Mr. Lieberman, her Senate mentor, she said: "I don't look at myself as taking his place. I hope to add another voice."
Ms. Collins said she thought it might have made a difference had Mr. Lieberman joined the three other senators in calling for a special committee to look into the administration's response to the Benghazi attack. "But not surprisingly he felt, correctly in my view, that there was no need for a special committee," she said.
The amigos say they will miss their travels, watching Borat films, walking together after dark on Friday nights instead of driving so Mr. Lieberman could observe the Sabbath, and visiting with troops.
Mr. Lieberman remembers in particular going to Vietnam with Mr. McCain, who spent more than five years in prison there after his plane was shot down over Hanoi. "Going with McCain to the Hanoi Hilton for me was quite an emotional experience," Mr. Lieberman said, noting that there is a statue of Mr. McCain where his plane was shot down.
"We complained to our Vietnamese hosts that the statue was much too small and not at all grand enough," he said. "They claimed they would replace it."
This article originally appeared in The New York Times.