WASHINGTON — As Election Day edges close and most members of Congress yearn to flee Washington, Senator John McCain of Arizona is more present than ever.


Only there is a new iteration of the Republican lawmaker and defeated presidential candidate who has been a constant in the capital even as he regularly transforms himself. Absent is the maverick who bucked his party on the environment and campaign finance, and verbally towel-snapped Republicans and Democrats alike on the Senate floor.


Gone, too, is the far-right leaning Mr. McCain of 2010, who found himself in a primary fight back home that caused him to retreat from his stances on immigration and global warming.


Mr. McCain instead appears to have entered Version 3 of his long and multipronged Senate career — partisan warrior and party stalwart. He takes to the Sunday TV talk shows, the Senate floor and the Capitol hallways that are filled with more reporters than mosquitoes at a garden party to press his party’s agenda on taxes, military spending and national security.


He walks largely in step with Senator Mitch McConnell of Kentucky, the Republican leader with whom he previously had an adversarial relationship that went all the way to the Supreme Court.


“Senator McCain is a tremendous leader in the Republican conference as well as a trusted adviser to me on a number of critical matters, including national security and fiscal issues,” Mr. McConnell said. “Being on the same side of these recent battles has not only strengthened our friendship, but it’s helped clarify the broader debate.”


This latest John McCain has emerged in the aftermath of a stinging loss in the 2008 presidential campaign to a man he considered to have a very thin résumé compared with his decades of military and public service, a loss that left him bitter about politics and the news media — a group he once jokingly referred to as his political base.


Now, after nearly three years of sniping from the sidelines, Mr. McCain is a polestar on nearly every major issue consuming the Senate, from a cybersecurity bill to the debate over Syria to an investigation into national security leaks and the fight to head off $500 billion in Pentagon cuts. He is arguably the most active senator in a frequently sleepy chamber.


Often these days, he actually smiles.


“It took me three years of feeling sorry for myself,” Mr. McCain said to a group of reporters this week as he held court outside the polished doors of a waiting senators-only elevator, taking questions as he does daily on the major topics of the day, be it the budget, the Arab Spring, postal reform or the reshuffling of Marines in Okinawa and Guam.


Mr. McCain was in all of his McCain-ness recently on the Senate floor, where he derided a group of House Republicans for suggesting that a top aide to Hillary Rodham Clinton, Huma Abedin, was connected to the Muslim Brotherhood. 


Next week, he will roll through a series of East Coast cities, holding town-hall-style meetings to speak out against planned cuts to the Pentagon that resulted from last year’s debt-ceiling deal, another core fight in which he is front and center.


In some ways it seems as if Mr. McCain remains unable to reconcile the rightward lurch he took two years ago with his clear desire to continue to put his stamp on myriad issues — at times bridging partisan divides — to burnish his legacy.


For instance, on campaign finance — an issue he was so personally associated with that his name was tied to the legislation that Mr. McConnell fought at the Supreme Court — Mr. McCain has been unwilling to work with Democrats on new bills to force more disclosure of the names of wealthy donors.


“I’ve been disappointed,” said Senator Richard J. Durbin of Illinois, the No. 2 Senate Democrat. “I was hoping John would carry that forward, but so far with the Disclosure Act and other things we’ve got on the floor he has not joined us. I just hope he goes back to his roots.”


Many of Mr. McCain’s other interests align neatly with the big issues of the day, particularly the debate over the role of the United States in conflicts in the Middle East — in which he has largely been a staunch critic of the Obama administration — and the planned Pentagon cuts.


The pattern is similar to that of other unsuccessful presidential candidates, like Senator John Kerry of Massachusetts, who publicly sulked for a few years before becoming a major player on Afghanistan and other issues.


“I just think a lot of it has to do with the agenda,” Mr. McCain said of his re-emergence, in an impromptu interview with several reporters. “After I lost, I knew that the best way to get over it was to get active.” (Mr. McCain, who disputed some coverage of him by The New York Times during the 2008 campaign, has a policy of not speaking directly to reporters from The Times.)


Senator Carl Levin, the Michigan Democrat and Armed Services Committee chairman who is working with Mr. McCain on a way to avoid Pentagon cuts, said that Mr. McCain was a “key spokesman” on the issue.


“It’s all relative around here in terms of partisanship,” Mr. Levin said. “Inside his party he stands shoulders above in terms of being willing to deviate from the grip of an antitax pledge.”


Mr. McCain is also a very useful advocate for his party in an election year. He provides credibility on military issues and can employ his rhetorical gifts on the Sunday talk shows (where he has appeared more than any other member of Congress this year, according to a tally by the Capitol Hill newspaper Roll Call) to promote the party view in a way that Mr. McConnell and others cannot.


“He loves his job,” said Senator Lindsey Graham, Republican of South Carolina and a longtime friend and ally of Mr. McCain’s. “He’s the template for someone in the future who runs for president and falls short. He didn’t take his ball and go home. I am just very proud of him. He’s very, very involved in all the things that really matter around here.”