WASHINGTON (AP) — Sen. John McCain is waging another national campaign — this time, to define his legacy.

After two unsuccessful presidential bids, the 78-year-old former Navy pilot and Vietnam prisoner of war has rebounded as the chairman of the powerful Senate Armed Services Committee. The post gives the Arizona Republican a significant say on national security issues — and a chance to ensure that his loss to Barack Obama in the 2008 White House race isn't the final word in the colorful McCain chronicles.

McCain wants to prod the Obama administration, which he derides as feckless, to adopt a tougher policy against worldwide threats. He wants budget and spending changes at the Pentagon.

A defense hawk in a party with a growing number of noninterventionists — he once dismissed a few as "wacko birds" — McCain wants to help educate new senators. McCain is calling foreign policy luminaries to share their world views with the committee, beginning this week with former national security advisers Zbigniew Brzezinski and Brent Scowcroft.

Ask McCain what he wants people to think of when they will recall his chairmanship.

Then ask how he wants to be remembered generally.

The answers are nearly identical.

"To be able to play a significant role in defeating the forces of radical Islam that want to destroy America," he says to the first.

To the second: "That I made a major contribution to the defense of the nation."

McCain clearly wants the chairmanship to help define his legacy, before voters in 2016 get the chance again to decide control of the Senate. The senator turns 80 that year, and all signs point to McCain running for a sixth Senate term.

The leadership role gives McCain new power to push his agenda. He still has the energy that has helped him survive a hard-to-makeup biography: three plane crashes, an aircraft carrier fire, five torturous years in captivity in Vietnam, nearly three decades in the Senate, and two presidential campaigns in 2000 and 2008.

"You will see, probably, the busiest Senate Armed Services Committee that you've ever seen," McCain said in a recent interview.

Some members of the administration are eager to reset the sometimes-tense relations with the blunt-spoken, dry-humored senator. After all, knotty international issues, such as the prospect of using force against Islamic State militants, fall within the purview of McCain's committee.

McCain and Vice President Joe Biden are genuine friends from serving two decades together in the Senate, though it's clear that Biden hasn't forgotten "some interesting things he's said about me, publicly" — such as McCain's suggestion in 2012 that Obama drop Biden as his running mate.

"I know he loves me. And I care about him, I really do," a chuckling Biden said of McCain in a recent telephone interview. "I think John's legacy is that he never quits."

McCain has a similar relationship with Secretary of State John Kerry, also a former Senate colleague.

Last April, during a hearing, McCain ripped into Kerry for "talking strongly and carrying a very small stick — in fact, a twig" on foreign policy. Kerry rejected what he said was McCain's "premature judgment about the failure of everything."

For all his partisan bluster and fierce conviction, McCain has a record of deal-making so established that it inflames some on the political right, Kerry said. The pair, both decorated Vietnam veterans, played key roles when President Bill Clinton normalized relations with Vietnam in 1995. More recently, McCain's been a member of bipartisan Senate groups that worked out deals on judges and immigration, though a bipartisan immigration reform measure passed by the Senate stalled in the House.

"He's a guy you want fighting with you if you can find a way" to compromise, Kerry said in a statement to The Associated Press. "This moment is a big one for him, and he has the capacity to really make a deep impact."

McCain is a frequent target of the right, who complain about his work with Democrats, from the late Massachusetts Sen. Ted Kennedy to Democrat-turned-independent Sen. Joe Lieberman of Connecticut.

On the Pentagon, McCain is looking to a longtime role model, Arizona Sen. Barry Goldwater, who returned to the Senate after losing the 1964 presidential rate and served as chairman of the Armed Services Committee.

McCain said the committee will tackle Pentagon restructuring. He also wants to end the automatic spending cuts that affected the military. Early next month, he expects the committee to confirm Ashton Carter as Obama's new secretary of defense.