Twenty senators — 10 Democrats and 10 Republicans — signed a statement announcing the framework deal. That indicated that the agreement could have enough GOP support to defeat a filibuster, the Senate supermajority rule that has impeded prior gun legislation.

“Families are scared, and it is our duty to come together and get something done that will help restore their sense of safety and security in their communities,” the statement read in part. “Most importantly, our plan saves lives while also protecting the constitutional rights of law-abiding Americans.”

Under the tentative deal, a federal grant program would encourage states to implement “red flag” laws that allow authorities to keep guns away from people found by a judge to represent a potential threat to themselves or others, while federal criminal background checks for gun buyers under 21 would include a mandatory search of juvenile justice and mental health records for the first time.

Other provisions would prevent gun sales to domestic violence offenders beyond just spouses, closing what is often called the “boyfriend loophole”; clarify which gun sellers are required to register as federal firearms dealers and, thus, run
background checks on their customers; and establish new federal offenses related to gun trafficking.

The agreement does not include a provision supported by President Biden, congressional Democrats and a handful of Republicans that would raise the minimum age for the purchase of at least some rifles from 18 to 21. Handguns are already subject to a federal 21-and-over age limit.

Other provisions would funnel billions of new federal dollars into mental health care and school security programs, funding behavioral intervention programs, new campus infrastructure and armed officers. One cornerstone of the deal is legislation sponsored by Sens. Roy Blunt (R-Mo.) and Debbie Stabenow (D-Mich.) to establish a nationwide network of “community behavioral health clinics,” though the framework does not yet include an agreed funding level for that program or others.

The announcement Sunday represents the fruit of a crash bipartisan effort launched in the days after the May 24 killing of 19 children and two teachers inside Robb Elementary School in Uvalde, Tex., which itself came 10 days after a mass shooting inside a Buffalo supermarket.

It also comes one day after thousands attended pro-gun-control rallies across the country organized by the student-led March for Our Lives group, including a Washington event on the National Mall. Sunday is also the sixth anniversary of one of the country’s deadliest mass shootings, the 2016 killing of 49 people inside the Pulse nightclub in Orlando.

Ahead of Sunday’s announcement, senators had publicly sketched out their negotiating positions in general terms.

Chris Murphy (D-Conn.), who has led Democrats’ efforts on gun legislation since the 2012 school shooting in Newtown, Conn., said during an anti-gun-violence rally Friday that he was determined to break congressional stasis on gun legislation, but not at any cost: “I’m not interested in doing something unless that something is going to save lives, unless that something’s going to be impactful and meaningful.”

Meanwhile, John Cornyn (R-Tex.), who has an A-plus rating from the National Rifle Association, said last week that he is interested in forging a compromise, but only if it preserves gun owners’ rights under the Second Amendment.

“This is not about creating new restrictions on law-abiding citizens,” he said. “It’s about ensuring that the system we already have in place works as intended.”

Key pitfalls remain: The framework announced Sunday amounts to a statement of principles, not a fully written bill. While people involved in the process said last week that significant chunks of the legislation have already been written, new points of friction frequently arise in Congress as the drafting process is finalized.

Red-flag laws, in particular, have raised many conservative Republicans’ hackles, though negotiators said last week that they believed there would be sufficient GOP support to pass any deal. The “boyfriend loophole” and firearms licensee provisions have also been subject to prior bipartisan talks that did not produce agreements.

“The details will be critical for Republicans, particularly the firearms-related provisions,” said a GOP aide familiar with the talks. “One or more of these principles could be dropped if text is not agreed to.”

The Republican signers of Sunday’s statement were Cornyn and Sen. Thom Tillis (N.C.), who led the talks for the GOP, as well as Sens. Roy Blunt (Mo.), Richard Burr (N.C.), Bill Cassidy (La.), Susan M. Collins (Maine), Lindsey O. Graham (S.C.), Rob Portman (Ohio), Mitt Romney (Utah) and Patrick J. Toomey (Pa.). Democrats in the group included leaders Murphy and Kyrsten Sinema (Ariz.), as well as Richard Blumenthal (Conn.), Cory Booker (N.J.), Christopher A. Coons (Del.), Martin Heinrich (N.M.), Mark Kelly (Ariz.), Joe Manchin III (W.Va.) and Debbie Stabenow (D-Mich.). Sen. Angus King, a Maine independent who caucuses with Democrats, also signed.

Biden also indicated his support: “Obviously, it does not do everything that I think is needed, but it reflects important steps in the right direction, and would be the most significant gun safety legislation to pass Congress in decades,” he said in a statement released by the White House on Sunday.

Senate Majority Leader Charles E. Schumer (D-N.Y.) said he planned to “put this bill on the floor as soon as possible” once the legislative drafting is completed, a process that aides said could take several days. Minority Leader Mitch McConnell (R-Ky.) did not formally endorse the deal in a statement Sunday but offered encouragement to the negotiators: “I continue to hope their discussions yield a bipartisan product that makes significant headway on key issues like mental health and school safety, respects the Second Amendment, earns broad support in the Senate, and makes a difference for our country.”

The framework also won plaudits from gun-control advocates, including the Brady Campaign to Prevent Gun Violence and Everytown for Gun Safety, which cast the agreement as a historic breakthrough, even though it does not include the tougher measures those groups have long advocated.

Everytown President John Feinblatt said that, if enacted, the framework would be “the most significant piece of gun safety legislation to make it through Congress in 26 long and deadly years,” while Brady President Kris Brown called it “a 30-year breakthrough in the making” and “a historic, new beginning that breaks the stranglehold of the gun industry.”

“In a less broken society, we would be able to require background checks every single time someone wants to buy a gun, and we would ban assault rifles outright,” said March for Our Lives co-founder David Hogg. “But if even one life is saved or one attempted mass shooting is prevented because of these regulations, we believe that it is worth fighting for.”

A National Rifle Association spokeswoman did not immediately respond to a request for comment Sunday.

House Speaker Nancy Pelosi (D-Calif.) signaled Friday that the Democratic-controlled House would move to enact whatever bill the Senate managed to pass. “If it’s life-saving and can make a difference, and they have bipartisan support for it, then we would welcome it, even though it won’t be everything that we want,” she said at a news conference.

The House has passed four gun-related bills that go considerably further than the tentative Senate deal. Last year, lawmakers passed a bill expanding federal background checks to all commercial transactions, including those conducted at gun shows and over the internet, as well as a measure extending the period the FBI has to complete background checks of prospective gun buyers.

Also last week, in response to the recent shootings, the House passed bills that banned sales of many semiautomatic rifles to those under 21, banned high-capacity magazines and promoted red-flag laws in both state and federal courts.

None of those bills has the requisite Republican support to pass the Senate.

The last substantial new federal gun-control laws were passed in the mid-1990s — the “Brady bill” of 1993, which created the national instant background check system, and the assault weapons ban of 1994, which outlawed some military-style semiautomatic rifles and handguns. The latter bill expired 10 years later and has not been renewed.

In recent decades, Washington has acted mainly to expand gun rights. In 2005, for instance, Congress immunized the firearms industry against product liability lawsuits, and in 2008, the Supreme Court enshrined an individual’s right to possess guns in the landmark case D.C. v. Heller. A 2013 push in the wake of the Sandy Hook Elementary School shooting to expand background checks to cover more gun transactions, including gun-show and internet sales, fell six votes short in the Senate.

In an interview Thursday, Murphy said he believed that the chamber had two weeks left to act — before lawmakers leave Washington for a two-week Independence Day recess.

But meeting even that timeline would require a framework for a deal to be put in place quickly, Murphy said, citing the likelihood that gun rights supporters in the Senate would seek to erect procedural hurdles to any potential legislation.

“We can’t come to agreement the last week we’re here,” he said. “There are people in the Senate that are no doubt going to use every rule available to them to hold this up and slow it down.”