When a gunman slaughtered 49 people at an Orlando nightclub in 2016, Sen. Marco Rubio, R-Fla., described it as a moment of revelation — a tragedy so grave that it helped prompt his decision to seek a second term.

A year and a half later, with no gun violence legislation having been enacted in the interim, Rubio is again at the center of a churning national debate about public safety and gun control. In a state now stricken by a second catastrophic shooting, Rubio is under intense scrutiny. So far, he has struck an unsteady balance between firmly supporting gun rights and appearing proactive in response to atrocities at home, with decidedly mixed results.

In a televised town hall-style meeting Wednesday night on CNN, Rubio gamely strained to convince grieving parents and students from Parkland, Florida, that they should view him as an ally. He suggested he might back specific new regulations on weaponry, perhaps including a ban on high-capacity magazines, which allow a gunman to fire a huge number of rounds without reloading.

But in a lengthy and emotional colloquy with Fred Guttenberg, whose daughter died in the shooting at Marjory Stoneman Douglas High School, Rubio politely refused to endorse a ban on assault weapons, drawing jeers from the audience and visibly frustrating Guttenberg.

Rubio leaned further into a different idea Thursday, saying in an interview that he might file legislation to ban certain large magazines, though he acknowledged that he had yet to settle on a specific proposal or discuss the idea with Sen. Mitch McConnell of Kentucky, the majority leader.

“I hope that we can put together a package that I intend to be in the lead on, together with others,” Rubio said.

Rubio may face intense skepticism in that germinal effort from Democrats — who see him as frequently feinting toward political independence but seldom actually breaking with his party — and from fellow Republicans who are uncertain of his plans and motives. Absent support from McConnell and President Donald Trump, who have not backed magazine restrictions, it is not clear Rubio has the clout to bring any such proposal to the Senate floor.

A former presidential candidate once known for his flourishing rhetoric and promises of political transformation, Rubio stressed that he is now focused on narrow and incremental ideas that might stand a chance of becoming law. He warned against “heading down the same path” lawmakers followed after the Pulse nightclub shooting in Orlando in 2016. At the time, Rubio proposed stopping gun purchases for people who had appeared on a federal terrorism watch list in the previous decade, but that idea went nowhere.

Rubio also supports raising the minimum age to purchase semi-automatic rifles from 18 to 21, an idea he said he mentioned to Trump on Friday when they flew together on Air Force One from Washington to West Palm Beach. The change has become necessary to update older laws that did not envision the widespread use of AR-15s and similar weapons in mass shootings, Mr. Rubio said.

“I’ve never advocated for that in the past, because it largely has never been an issue before,” he said. “Our laws today reflect a time when dealing with gun violence was largely keeping handguns out of the possession of a gangbanger or street thug or what have you.

“Obviously since this increase in mass shootings and the epidemic we now face, it’s now become more of a semi-automatic rifle-based tragedy, so our laws have to change to reflect that.”

Whether Rubio has found himself back in the spotlight as a matter of chance, or placed himself there as a political choice, is a matter of some debate among his fellow Republicans, as well as some Democrats in Congress who would welcome his backing even for incremental gun measures. Students who disagreed with Rubio nevertheless thanked him for attending the televised meeting, unlike Trump and Gov. Rick Scott, who did not accept invitations from CNN.

Rep. Charlie Crist of Florida, a Democrat and former Republican who was once Rubio’s bitter rival in a Senate primary, said Rubio’s comments Wednesday night offered reason for optimism.

“I’m encouraged by that, to be honest, and I hope that that evolution continues,” Crist said Thursday. “In the wake of an event such as this, that can happen.”

Crist, a former ally of the National Rifle Association who now supports a ban on assault weapons, said much of Florida had undergone a similar reassessment of gun rights orthodoxy after two massacres in the state that targeted young people.

Yet a mood of skepticism pervades discussion of Rubio in both Washington and Florida: The senator has amassed a reputation over the past year as a kind of permanently anguished Republican, musing repeatedly in anxious tones about breaking with his party on matters of conscience, but never quite following through.

A Democratic lawmaker who joined Rubio at the town hall, Rep. Ted Deutch — whose district includes Stoneman Douglas High — suggested Rubio was open only to “legislation that the NRA can live with,” which Deutch called inadequate.

Rubio, in both the town hall and a subsequent interview, fiercely disputed that he operates with deference to the NRA. He insisted, however, that the people who lived through the Parkland shooting were pursuing an unrealistic goal in pushing a ban on assault weapons, which he called both ineffective and politically implausible. “If that is what the expectation of what action is by some, they’re going to be disappointed,” Rubio said.

During the town hall, Rubio drew boos by refusing to reject political support from the NRA. And he told Guttenberg that a more effective focus than banning assault weapons would be to “make sure that dangerous criminals, people that are deranged, cannot buy any gun of any kind.”

Guttenberg, who told Rubio that his daughter, Jaime, had been shot in the back with a “weapon of war” while fleeing the Parkland gunman, was plainly frustrated. “Your answer speaks for itself,” he said.

Participating in the CNN event, Rubio’s allies said, reflected both his sense of duty and perhaps a certain masochistic streak in his personality. There were no illusions within his circle that Rubio would not face indignant and sometimes hostile questions — and loud jeers on national television — but Rubio decided to proceed all the same.

“No one forced me to run for re-election — I wasn’t even going to,” Rubio said today. “I chose this job, and I voluntarily chose to be in this position, because I want to make a difference.”

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