Christopher S. Murphy has made championing gun safety his mission as a senator from Connecticut. And the Democrat has committed to campaigning this fall for candidates and ballot measures that will change the issue’s political calculus.

But two prominent groups normally aligned with Democrats on the issue aren’t making things easy for Murphy or his party with their endorsement of Sen. Patrick J. Toomey, a vulnerable Republican whose Pennsylvania seat will likely be key to which party controls the Senate next year.

Murphy himself acknowledges the complexity of the situation.

“If you are working on the issue of protecting Americans from gun violence, you have a lot of reasons to thank Pat Toomey,” he said at a National Press Club luncheon Thursday afternoon.

[For Toomey, Gun Deal Is Good Politics]

That’s exactly what Americans for Responsible Solutions, the gun safety group founded by Murphy’s former House colleague, Democrat Gabrielle Giffords of Arizona, did when they endorsed Toomey for his efforts on a bill in 2013 that would have provided background checks for firearms. Toomey worked with several Democrats, most prominently West Virginia’s Joe Manchin III, on the bill, but it stalled in the Democratic-controlled Senate.

And that’s in addition to the endorsement by Independence USA, the super PAC founded by former New York Mayor Michael Bloomberg. That group ran ads in Pennsylvania in favor of Toomey, including one featuring Erica Smegielski, the daughter of slain Sandy Hook principal Dawn Hochsprung, who thanked Toomey in the ad for his efforts.

Several survivors and family members of victims of the horrific 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, were present at the lunch in the Press Club’s Holeman Lounge, lending an emotional element to the “newsmaker” event. Asked in front of them whether he would campaign for Toomey’s opponent, Democrat Katie McGinty, Murphy paused to give credit to Toomey.

“Pat Toomey did something that was exceptional in reaching out and working with Democrats on this issue,” he said.

[Democrat Launches Fund to Support Gun Control Candidates]

Murphy had a fine line to tread, to acknowledge the good he sees there. But he’s still, ultimately, going to try to get Democrats in the majority. And that means working against the campaigns of people like Toomey.

“I don’t just work on this issue. I work on lots of other issues as well. And I’m supporting Katie McGinty, and I will be supporting her from now until Election Day because, though I appreciate what Pat Toomey did on the issue of background checks, there are a lot of other issues to which I deeply disagree with him,” Murphy said. “And so long as Republicans are in charge of the United States Senate, good luck getting these votes on the floor of the Senate in the absence of extraordinary measures like the filibuster.”

That reference to his nearly 15-hour filibuster in June to try to force votes on gun safety measures helped launch Murphy into the country’s political consciousness. His actions helped land floor votes on measures expanding background checks and a ban on gun sales to suspected terrorists. Each measure fell short though, providing Murphy a poignant reminder of his party’s place in the minority.

[Pennsylvania Senate Race Could Come Down to Guns]

As his Press Club comments indicate, the political considerations aren’t easy ones for him.

“That being said, I don’t think we are going to make progress on this issue if all we do is try to elect Democrats,” Murphy said. “I do think that we have to be honest about Republicans who have stuck their neck out. Some of my friends get upset when I acknowledge that Pat Toomey did something that was mildly heroic when he worked with Democrats on background checks, but that’s the truth. He did. And we should congratulate and applaud Republicans when they do work with us.”

But that doesn’t mean Toomey gets a free pass when Murphy is filling out his political travel schedule for the fall.

“There are some key elections out there that pundits and political prognosticators are going to look to when they decide whether or not guns were on the ballot in 2016 and which side won,” he said. “And so I’m going to be spending much of my time between now and the election traveling to the states in which we have a clear difference between candidates for the Senate and the House on the issue of guns.”