Sens. John McCain (R-Ariz.), left, and Chuck Schumer, (D-N.Y.), center, have forged a relationship amid their calls for an investigation into Russian hacking efforts during the presidential election. (J. Scott Applewhite/AP)

Sens. John McCain and Charles E. Schumer used to have a lousy relationship. The Arizona Republican and New York Democrat came from different backgrounds and focused on distinct legislative priorities. They were two hard-charging senators who were both aggressive in their courtship of the media.

The New Yorker and the Arizonan even broke into an open feud when, during a 2011 debate on defense policy, McCain joked that Long Island was “regrettably part of the United States of America.” Schumer demanded an apology: “All of America saw how heroic Long Islanders were on 9/11.”

Five years later, times have changed. The duo is emerging as a potentially critical force in the new world order of President-elect Trump and a Republican-controlled Congress. In the last 10 days, McCain, chairman of the Senate Armed Services Committee, and Schumer, the incoming Senate minority leader, led a bipartisan push to create a robust investigation into Russian hacking of political committees that intelligence officials say was designed to promote Trump’s candidacy.

Through TV appearances and joint letters, the senators are pushing for an investigation that Trump is so far rejecting and other Republicans have been reluctant to tackle because such a probe might appear to undermine the results of the 2016 elections.

“There’s no doubt [the Russians] were interfering,” McCain said Sunday on CNN’s “State of the Union,” stepping up the pressure on congressional GOP leaders. The question is now, how much and what damage? And what should the United States of America do?”

An hour or so later, Schumer held a news conference in New York City echoing McCain’s call for a detailed investigation, and a few hours afterward the carefully choreographed effort included a formal letter from McCain, Schumer and two senior senators on foreign policy issues, Jack Reed (D-R.I.) and Lindsey O. Graham (R-S.C.), asking Senate Majority Leader Mitch McConnell to establish a select committee to conduct a thorough investigation.

It’s unclear whether they will be successful in their quest, as McConnell (R-Ky.) and House Speaker Paul D. Ryan (R-Wis.) have said any such probe will be handled by their chambers’ Intelligence committees.

[Congress can’t decide how to probe charges Russia aimed to help Trump]

But this latest act in a budding McCain-Schumer partnership could turn into a repeat performance in the new Trump era, on issues including national security, immigration and even the institutional work of the Senate.

Each has a more powerful perch than previous years. Schumer is taking over his caucus at a time when he will be considered the most powerful Democrat in Washington. McCain will be sworn in Jan. 3 to a seventh term after a blowout victory over his opponent that far exceeded Trump’s narrow Arizona win, giving McCain a wide berth to make decisions without fear of political backlash. Additionally, Trump at times insulted McCain during the campaign, so the incumbent owes no favors to the incoming president.

Schumer and McCain could not seem much more stylistically different, but the two have a common ability to command the spotlight and shape debates inside the Capitol, something that becomes exponentially more powerful if they are working on the same side.

McCain, 80, is a hero from his time as prisoner of war during the Vietnam War, a five-and-half-year stint during which Schumer, 66, attended Harvard University, graduated and then began his studies at Harvard Law.

Schumer was elected to the House in 1980 from his native Brooklyn, and McCain came along two years later after having moved to the Phoenix area and won a Republican-leaning district. Schumer’s focus was always on legal matters, crime and gun control; McCain’s was on national security.

McCain won his Senate seat in 1986 and set off on a long march to try to become president, running unsuccessfully in 2000 and then winning the Republican nomination in 2008 before losing to President Obama. Schumer won his Senate seat in 1998 but never had any greater ambition than to become a powerful senator.

McCain’s early view of Schumer was as a partisan with sharp elbows. He oversaw the Democratic Senatorial Campaign Committee and added 14 seats to the Democratic caucus in four years. When McCain suspended his 2008 campaign to fly to Washington to try to help cinch a Wall Street rescue package, the meeting ended in insults and no deal. [Senate reaches tentative deal on filibusters]

In a Senate-floor speech the next day, Schumer took direct aim at McCain and blamed him for the faltering talks. He said McCain could help in only one way: “Get out of town.”

The first thaw in their relationship, according to those close to the senators, came when a large group of senators started discussing Senate rules on presidential nominations four years ago, the first of two Schumer-McCain negotiations that delayed for a few more months a Democratic move to end filibusters on most nominees. A few weeks after those first talks, they joined forces again as the leaders of a bipartisan group of eight senators that wrote legislation to revamp immigration laws and increase border security, which culminated in a 68-to-32 vote approving the measure.

They spoke so much that year that Schumer knew McCain’s phone number by heart and blurted it out during a video interview with Politico, prompting the producers to bleep out the numbers. But their work on immigration died in the House, where conservatives would not allow a debate on the issue.

Now, they’re back together again. McCain has been careful to keep McConnell in the loop about his moves with Schumer, but he has made clear that he won’t let the matter of alleged Russian interference in the elections just drop. McCain has always viewed Russian President Vladi­mir Putin with deep suspicion.

He is now trying to balance his work with Schumer to forcefully investigate the latest accusations while also reassuring Republicans that he’s not trying to overturn Trump’s win.

“I have seen no evidence that the election would have been different,” McCain said on CNN. “But that doesn’t change the fact that the Russians and others, Chinese to a lesser degree, have been able to interfere with our electoral process.”

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