A year ago, Sen. Mark R. Warner toiled in the shadow of his fellow Virginia Democrats.

While Tim Kaine barnstormed the country as Hillary Clinton’s running mate and Terry McAuliffe burnished his national profile as chair of the National Governors Association, Warner was casting about for a signature issue.

Then came the Russians — and Warner, 62, was suddenly facing the most important work of his public life.

As the top Democrat on the Senate Intelligence Committee, he has forged an unusual partnership with his Republican counterpart, Richard Burr of North Carolina. Together they are steering the most significant of four congressional investigations into possible Russian collusion with President Trump’s campaign.

Their work will be on display before the nation Thursday, when former FBI director James B. Comey makes a highly anticipated appearance before their committee — his first public testimony since his firing by Trump.

Warner’s reputation as one of the most bipartisan politicians on Capitol Hill is undergirding the credibility of the Senate probe, observers say.

“Democrats can raise hell until the cows come home; Mark is going to make sure the facts are there,” said Sen. Joe Manchin III (D-W.Va.), one of his closest friends in the Senate. “This is not a witch hunt. He’s not going to let that happen.”

In the months since the investigation launched, Warner has become a frequent guest on the Sunday morning shows. Reporters mob him in the Capitol hallways. Secure phone lines were installed in his Alexandria home. His cellphone is encrypted. He has less time for long bike rides, and he has a few more gray hairs.

He justifies the need to investigate the administration this way: In the four months since Trump took office, he has fired acting attorney general Sally Yates; Preet Bharara, the U.S. attorney for the Southern District of New York; and Comey — all of whom were investigating his campaign or administration — and former national security adviser Michael Flynn was forced to resign.

“If there is no there there — and that is what the administration keeps saying — they’re certainly not acting like it,” Warner recently told a Richmond business crowd.

Kaine, who was Virginia’s lieutenant governor when Warner served as governor from 2002 to 2006, said the investigation consumes his friend.

“I see him more seized by responsibility on this particular item than anything that I’ve ever seen in the 37 years that I’ve known him,” said Kaine, who met Warner in 1980 when they were both students at Harvard Law School.

“There will be Democrats who will go out and just on their own blister the hide off the other side. Mark is very mindful of the fact that this investigation, if it’s too partisan, it could just blow up,” he said.

One Democrat suggested this could be Warner’s “Caldwell Butler moment,” referring to the GOP congressman from Virginia, now deceased, who helped draft the articles of impeachment against President Richard M. Nixon.

“Here’s the guy who was pushed to the back of the room who’s now pushed to the front of the room,” said Steve Jarding, who ran Warner’s 2001 campaign for governor. “It couldn’t be better timing for a nonpartisan leader.”

A good fit

Burr, the chairman of the Senate panel, and Warner have remained on the same page publicly, aside from an early misstep.

In January, Burr said the committee would not delve into communications between Trump associates and Russia, but the next day he and Warner jointly announced that the investigation would look at those links, suggesting something — or someone — changed the Republican’s mind.

“We together, with the members of our committee, are going to get to the bottom of this,” Warner said during a March news conference, his hand on Burr’s shoulder.

Burr, who is not seeking reelection, declined an interview but released a statement praising Warner as “a valued partner” who is “integral to the committee’s efforts.”

“We are both committed to following the facts where they lead and providing the American people the opportunity to make their own judgments,” he said.

Lawmakers from both parties have described them as the adults in the room.

“Mark will be critical of the administration when he thinks it’s right to do so,” said Republican Saxby Chambliss, the conservative former senator from Georgia. “He and Senator Burr have disagreements, but they’re able to do so in a professional way.”

Unlike other panels, the top Democrat is not the “ranking member,” but the vice chair. If Burr is absent, the gavel goes to Warner, not another Republican. Many votes are unanimous or close to it.

It also benefits Warner to have a friend in Senate Minority Leader Charles E. Schumer (D-N.Y.).

“Senator Warner has shown both persistence and patience, and the committee is in a very good place right now, in no small part because of Senator Warner’s work,” Schumer said in a statement.

Virginia political insiders say the committee is a good fit for Warner, a self-proclaimed “radical centrist” who mentions more Republicans than Democrats in speeches and urges Democrats to vote for deserving Republicans.

“People say, ‘Oh, Warner, we love [that] you’re bipartisan.’ Well, reinforce that. Neither side has a monopoly on truth,” he said in Richmond.

It’s a worldview he embraced when he ran for governor in 2001 as a multimillionaire former venture capitalist from Northern Virginia, courting voters that Democrats had ignored in rural southwest and Southside Virginia.

With the “Bubba strategy,” the campaign famously used a bluegrass jingle, NASCAR sponsorship and “Sportsmen for Warner” as cultural currency to gain entree into venues where Warner could pitch an economic message.

Once in office, he closed a $6 billion budget gap and raised taxes by charming Republicans so deftly that GOP lawmakers still resist working with Democrats in Richmond out of fear of creating another Mark R. Warner.

After abruptly abandoning a presidential bid, he won election to the Senate in 2008 and began a rocky transition from high-energy chief executive to freshman lawmaker.

“Neither one of us have been blessed with patience. As governor, you need to get something done every day,” said Manchin, another former centrist governor who stayed in Warner’s Alexandria guesthouse when he joined the Senate.

‘Your finest hour’

Warner used words such as “debacle” and “embarrassment” to describe how Congress handled the 2008 financial crisis and sequestration, but he found a tribe with the bipartisan Gang of Six, which tried to come up with a budget deficit fix.

They met in three-hour weekly sessions on Capitol Hill and at Warner’s stately home, where he grilled steaks.

Regardless of the hour, Warner would not let anyone leave if he felt the group was close to a breakthrough, Chambliss said.

“He is a person who does want to get things done irrespective if it’s a Democratic idea or a Republican idea,” said Chambliss, who remains close to Warner.

But with little support from legislative leaders, such as then-Senate Majority Leader Harry M. Reid (D-Nev.), who dismissed the group’s work as “happy talk,” the effort failed. (Through a spokeswoman, Reid declined an interview for this article.)

Warner made no secret of his frustration with the tradition-bound chamber, and the comments haunted him as he nearly lost reelection in 2014 to longtime Republican strategist Ed Gillespie, who is now running for governor.

“My occasional dissatisfaction with the Senate I sometimes wore on my sleeve too much,” he said, without acknowledging fault.

Critics said Warner failed to grasp the changing demographics of Virginia, where McAuliffe won statewide by tacking to the left and demonizing the GOP. Instead, Warner touted the endorsement of his predecessor and mentor, longtime Republican senator John Warner, and spread a relentlessly bipartisan message.

Warner “may have been using more the older playbook,” Jarding said. “You try to run the next race based on the last one. It almost never works.”

Warner rejects this narrative, noting that he was the only Democrat who won statewide in the South or the Mid-Atlantic in a GOP wave year.

Returning to the Senate with a victory margin of less than one percentage point, Warner embarked on an ambitious project to remake capitalism in the age of the gig economy. Not the sexiest of issues, but it engaged him intellectually.

His plans changed drastically, however, when Trump won and the top Democratic slot on the Intelligence Committee landed in his lap.

“I told him, ‘This is going to be your finest hour, this committee,’ ” said JohnWarner, 90, whose seat Warner holds.

Fun friend, demanding boss

For all his hard-charging seriousness, Warner is still the gregarious ringleader among his friends and a night owl who has a dinner on his schedule most nights a week.

Thousands attend a pig roast he and his wife, Lisa Collis, host in big election years on their farm on the Rappahannock River.

On Halloween, Warner dresses as a mad chef with fake blood and dark eye shadow and gives out candy and olive “eyeballs” in spaghetti to a steady stream of children from all over Northern Virginia. It started with his three daughters — now in their 20s — and grew large enough that police close the street on the Alexandria waterfront.

An annual day-before-Thanksgiving tradition called the Pilgrims Lunch, going strong for 30 years, starts with basketball and ends with steaks and wine at the Palm restaurant in the District.

“It’s a big deal, and you want to stay on the list. Everyone who is important or thinks they’re important in Virginia politics shows up,” said Rep. Don Beyer (D-Va.), who has known Warner since the late 1980s.

After an interminable congressional dinner, Warner will call his friend Sen. Amy Klobuchar (D-Minn.) to dish. “He likes to have fun, which is really important because a lot of lawmakers can have a grim attitude right now,” she said.

Although many of Warner’s staff members are intensely loyal and have been with him for a long time, he can be a demanding boss.

As he boarded a cramped Senate office building elevator recently, an aide told Warner they were headed to the fifth floor. “I know that,” he snapped.

In the lobby of his office hangs a framed Time magazine cover story calling him one of the five best governors of 2005.

The following year he visited the early presidential primary states of Iowa and New Hampshire and raised $9 million, but he worried how the campaign would interfere with his family life.

That was the last time he was in the national spotlight — until now.

If the fire in the belly was missing then, he’s full of energy these days.

At the Capitol, rather than wait for an elevator, he asked a companion, “How are your shoes?” and sped down the stairs without waiting for an answer.