“It’s incredibly heavy to be surrounded by such tragedy,” Murphy said in an interview. “I feel a real weight that if by the time my political career is done, we haven’t made significant progress on this issue, my time in Washington will be a failure.”

It’s not for lack of trying. Gun control is no pet project for the 47-year-old, who won his first election to the House at age 33. Murphy calls it the issue he’s “most passionate about” and “the motivating force for” much of his political career.

But, he added, “every single day, I wish there was a different” topic driving him forward.

The day before that remarkably candid interview, Murphy had stood on the National Mall alongside other lawmakers to unveil 40,000 white flowers in commemoration of the lives lost to gun violence this past year. The flowers were planted by the group named for his friend and gun control ally, former Rep. Gabby Giffords, who stood with him. Speaker Nancy Pelosi was there, too, with high praise.

“We will have legislation because of [Chris] Murphy’s persistence,” Pelosi said at the event.

But as Murphy already knows, his tenacity may not be enough. And he’s already contending with an activist base that’s worried Democrats still can’t get anything done on guns.

“We didn’t work so hard in 2018 and in 2020 to elect a progressive Congress and White House to see nothing,” said Max Markham, policy director of the gun control group March For Our Lives.

Cameron Kasky, a graduate of the Florida high school where the 2018 shooting of 17 people inspired a cohort of energized and traumatized young gun control advocates, predicted a backlash against Democrats if they can’t act: “If Congress does not really put the pedal to the metal, then we’re gonna see really nasty things happen in 2022,” he said.

Many influential gun control groups are pressing for changes to the filibuster before anything else, seeing the Senate’s 60-vote threshold to pass most bills as the main obstacle to progress.

The Fix Our Senate coalition calling for the elimination of the filibuster includes gun control groups like Brady: United Against Gun Violence and March For Our Lives. A spokesperson for the bigger coalition, Eli Zupnick, said there was “no chance of meaningful gun safety legislation” with the legislative filibuster intact.

But Democrats don’t have the votes among themselves to end the filibuster. That leaves activists to put their faith in Murphy, viewing him as an honest broker who won’t make concessions they can’t swallow.

“Murphy’s always behind some of the best legislation that you’re going to see on guns,” said Kasky.

And despite his exhaustion with the endless cycle of good-faith attempts followed by collapse, Murphy is trying again. He worked the phones during the Senate’s spring recess, talking with what he estimated was close to half of the 50-member Senate GOP conference about background checks.

“I’ve had a lot of very encouraging conversations with Republicans over the last few weeks. I do see a path to 60 votes,” he said, adding that he told GOP colleagues he has “no interest in this issue becoming a permanent political cudgel” against them.

Among the Republicans whom Murphy called was Indiana Sen. Mike Braun, who recalled listening to Murphy’s case but was hesitant to accept a broader deal.

“Anything that’s going to make it more difficult for law abiding citizens to exercise their Second Amendment [rights], that’s not going to go anywhere,” Braun said.

Braun said that he’d be open to a narrower attempt but not the kind of comprehensive legislation Democrats want. The Indianan described retiring Sen. Pat Toomey (R-Pa.) as an anomaly for his past openness to bipartisan work on background checks.

Sen. John Cornyn (R-Texas), whom Murphy cited as a potential partner given their past collaboration on improvements to background check systems, also said he’d consider the idea of a narrower bill. Cornyn added that he appreciated the “sort of quiet conversations” he’s having with Murphy “to see where we can find common ground.”

Despite the faint stirrings of possible agreement, Murphy still has to lock in support from senators in his own caucus for whatever bill comes to the floor. That’s not a given: Sen. Joe Manchin (D-W.Va.) played a leading role in shaping the chamber’s failed 2013 background checks bill but has recently cast doubt on House-passed legislation to address the issue.

Murphy acknowledged a background checks bill might not advance this month, and that it could fail again even if it can get to the Senate floor.

He said he wanted to “give this a month or so,” hoping for a workable bill by the end of spring or early summer. And if Democrats don’t have a filibuster-proof compromise by then, “at some point you will have to call their bluff,” he said of Republicans.

One factor working in his favor is the waning influence of powerful gun lobby groups like the NRA, the once-influential organization now going through bankruptcy. The Democratic Party has also shifted leftward on guns as its number of red-state incumbents has dwindled.

“I don’t know … that we’ll have another opportunity like this” to act on guns, he said of Democrats’ slim majorities in both chambers of Congress.

He’s come a long way on the issue since ascending to the Senate in 2013, when guns were “a third rail issue for legislators,” said Mark Barden, the co-founder and managing director of the gun control group Sandy Hook Promise. Barden credited Murphy with helping change the national conversation around guns.

The senator “knows that this is a long game,” said Barden.

Murphy’s still playing that game. Even if background checks legislation fails again, Murphy sees the push for gun control as a “historic social change movement” in the same vein as the civil rights and marriage equality movements, both of which “suffered a lot of setbacks before they achieved victories.”

“I hope that we get something substantial done this year,” Murphy said. “But I also remember that from the time that [former White House press secretary] James Brady was shot to the day the Brady [gun control] bill passed the Congress, it was over a decade.”

Marianne LeVine contributed.