Even within their own party, Republican Sens. John McCain and Lindsey Graham now have to shout to be heard.

It's a stunning change for two men who have been the leading voices for their party's interventionist vision on foreign policy and now find themselves on the periphery of a debate over the conflict in Libya that is reshaping the GOP's stance on war and executive branch power.

Their staunch support of the effort conflicts with a chorus of leading Republicans: House Speaker John Boehner has threatened to pull funding for the Libya effort, Republican presidential hopefuls dug in during the national debate last week and several House Republicans even joined Democrats in filing a lawsuit against President Barack Obama for his decision to use force.

"In the foreign policy debate, realists are becoming a part of the Republican mainstream, and that makes Sen. McCain and Sen. Graham more than a little apprehensive," said Dimitri Simes, president and chief executive of the Washington, D.C.-based think tank Center for the National Interest.

McCain and Graham's new role as outsiders on Libya shows how their influence over the party's once-defining stance on foreign policy - held for the past two decades - is slipping away as the Republican Party zeros in on spending and a public grows weary of the mounting death toll from a decade at war.

But McCain and Graham aren't being co-opted. "Sen. Graham is speaking out. He's going to continue to be who he is," his spokesman, Kevin Bishop, said Monday.

Both senators took to the Sunday talk shows and issued apocalyptic warnings, saying the party's turn to "isolationism" - a derogatory and disingenuous term in the eyes of tea party types - could lead to more terrorist attacks against the U.S., the mass murder of innocent civilians and even a spike in oil prices.

"If you don't think [Libyan strongman Muammar] Qadhafi surviving doesn't affect American national security interests, we're just on different planets," Graham (R-S.C.) said on NBC's "Meet the Press." "If this guy survives, it's the end of NATO, our standing in the world goes down, Egypt gets overrun by refugees, and the mad dog of the Mideast, Qadhafi, is out of his cage, and you will see oil prices double."

In a separate appearance on ABC's "This Week," McCain repeatedly dismissed as "isolationist" the recent retreat by top Republicans from a more muscular foreign policy.

"We cannot repeat the lessons of the 1930s when the United States of America stood by while bad things happened in the world," the Arizona Republican said. "We are the lead nation in the world and America matters and we must lead, and sometimes that leadership entails sacrifice, sadly."

The Sunday shows may be a public pulpit, but they don't offer much insider sway. 

As the top Republican on the Senate Armed Services Committee, McCain still wields some power when it comes to the Libya conflict. Minority Leader Mitch McConnell (R-Ky.) has deferred to McCain on questions about Libya. And McCain and Foreign Relations Committee Chairman John Kerry (D-Mass.) have spent weeks fine-tuning a Senate resolution that would back Obama's use of force in the region. 

"As we continue to bleed blood and treasure from three wars, the Rand Paul arm of the Republican Party is on the upswing and the Graham-McCain crusading is less in favor," said Gene Healy, vice president of the libertarian think tank the Cato Institute, who blogged Monday about the GOP's foreign-policy divide. 

Boehner (R-Ohio) has threatened to cut funding for the Libya effort over a legal dispute with the White House over whether Obama requires congressional approval to continue limited U.S. operations under the War Powers Resolution. Votes could be held in the House this week. 

And at last week's debate in New Hampshire, GOP candidates seeking to replace Obama went further, questioning why America is involved in that nation's civil war. 

Rep. Michele Bachmann (R-Minn.), head of the House Tea Party Caucus who serves on the chamber's intelligence committee, pointed out that America was not attacked by Libya and therefore is of "no vital national interest." Businessman Herman Cain called the conflict in North Africa "an absolute mess." And former House Speaker Newt Gingrich called for a "totally new strategy for the region." 

Meanwhile, front-runner Mitt Romney set his sights on Afghanistan, arguing that "it's time to bring the troops home" and that the lesson from the decade-old conflict is that "Americans cannot fight another nation's war of independence." 

Those comments elicited a swift response from Graham, who warned last week that Republicans risk looking more like Jimmy Carter than Ronald Reagan on national security. On Sunday, McCain suggested that the Gipper - whose legacy is often invoked by candidates on the campaign trail - would be rolling in his grave if he heard the foreign policy views espoused by some in his party.

"I wonder what Ronald Reagan would be saying today?" McCain asked during an appearance on ABC's "This Week." "He would be saying that is not the Republican Party of the 20th century, and now the 21st century. That is not the Republican Party that has been willing to stand up for freedom for people all over the world, whether it be in Grenada or whether it be in our enduring commitment in countering the Soviet Union."

Invoking Reagan to take a swipe at other Republicans struck some GOP observers. 

"I remember Ronald Reagan saying not to speak ill of a fellow Republican," said Simes, whose group was founded by President Richard Nixon. "The fact that Graham is using this strident language is quite remarkable. Either he does not care about the fortunes of the Republican candidates or you have to believe he is becoming quite emotional and a little desperate. I don't see any other explanation." 

It's not only Graham and McCain who are taking seriously GOP threats to American interventionism. 

The neoconservative Foreign Policy Initiative on Monday released a letter signed by nearly 40 former government officials and foreign policy experts urging Congress not to reduce or cut funding for NATO-led U.S. military operations in Libya, which include intelligence, predator drones and refueling but no ground troops. 

"The United States should be leading in this effort, not trailing behind our allies," the group wrote. 

And when it comes to foreign policy, freshman Sen. Marco Rubio (R-Fla.) is swimming against the tea party currents that helped elect him last fall. Like McCain and Graham, he views the conflict in Libya as a question of national security rather than constitutionality. 

"For me, the equation is pretty straightforward. Muammar Qadhafi's hands are dripping in American blood. His own people want to get rid of him," Rubio told reporters last week. "To the extent we can help them do that, we should within the limitations that we have and in the national interest." 

Realists, however, point to recent polling that suggests Boehner, Romney and other mainstream Republicans may be onto something. A Pew Research Center survey released last month found that 55 percent of conservative Republicans believe the U.S. "should pay less attention to problems overseas and concentrate on problems here at home." That's up from 36 percent in 2004, in the midst of the Iraq and Afghanistan wars. 

"We ran that experiment, and after spending $1 trillion and 6,000 American deaths abroad, there is increasing mistrust of foreign interventionism among the public at large and within the Republican Party," Healy said. "When you have Newt Gingrich, who sees threats everywhere he looks, striking a note of restraint at the debate, you know something's going on. Boehner has a newfound affection for the War Powers Act because he can read the tea leaves."