The Senate passed a bipartisan package on gun safety Thursday night, ending a nearly 26-year impasse on the issue in the wake of a recent streak of major mass shootings.

The “Bipartisan Safer Communities Act,” which passed 65-33 after weeks of negotiations — and which is expected to become law, doesn’t go as far as many Democrats wanted. But it introduces tailored reforms meant to incentivize states to keep guns out of dangerous people’s hands, provide new protections for domestic violence victims, enhance screening for gun buyers under the age of 21, and crack down on illegal gun purchases and trafficking.

The bill also provides billions of dollars in additional funding for school safety and mental health resources. Democrats have stressed they don’t believe that America’s gun violence epidemic can be solved by investments in mental health resources, as Republicans have argued, but have said that they won’t pass up the opportunity to put more money towards mental health.

The last time Congress passed a major piece of gun legislation was in 1994, when it enacted a now-expired 10-year ban on assault weapons. Though there were attempts to pass gun control legislation in Congress following the 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, they failed. The recent mass shootings at an elementary school in Uvalde, Texas, and at a supermarket in Buffalo, New York created a renewed urgency for some federal action on guns.

Sens. John Cornyn of Texas (R-TX), Thom Tillis (R-NC) , Chris Murphy (D-CT), and Kyrsten Sinema (D-AZ) were the primary negotiators. Ultimately, 15 Republicans and 50 members of the Democratic caucus ended up joining them in voting for the bill.

“It’s taken a decade, because for too long Congress has failed to make meaningful progress on gun safety reform,” President Joe Biden said in a statement Thursday. “I call on Congress to finish the job and get this bill to my desk.”

The bill is expected to go there shortly, after a vote in the Democrat-controlled House.

What’s in the Senate’s gun control bill

Unlike the 1994 law, the bill doesn’t explicitly ban any weapons. Instead, it creates new rules around gun ownership and provides incentives to states to enact their own gun control measures.

The bill would allocate $750 million to supporting states in implementing extreme risk laws, or “red flag laws,” that temporarily prevent people who have been found by a court to pose a risk to themselves or others from obtaining a gun. Currently, 19 states and Washington, DC, have red flag laws. Most of these states are controlled by Democrats, with the exception of Florida and Indiana.

Research has suggested that such laws can prevent mass shootings, given that about half of mass shooters tell someone about their plans in advance and exhibit warning signs such as agitation, abusive behavior, depression, mood swings, an inability to perform daily tasks, and paranoia.

The bill would also close what’s called the “boyfriend loophole.” Under current federal law, only those who are convicted and are living with their partner, married to their partner, or have a child with their partner are barred from buying a gun.

Some states have already passed laws to partially or completely close the loophole, but this would do so at a federal level by prohibiting people convicted of domestic violence while in a “dating relationship” — defined as a “relationship between individuals who have or have recently had a serious relationship of a romanic or intimate nature” — from purchasing firearms. People convicted of non-spousal misdemeanor domestic abuse would be able to own a gun again after five years if they keep a clean record under the bill. But convicted spouses would still be banned from purchasing guns for life.

Gun buyers under the age of 21 would face enhanced background checks under the bill. They would be subject to an elongated, three-day initial review process of juvenile and mental health records, including checks with state databases and local law enforcement. If that initial review process turns up anything of concern, the buyer would have to undergo an additional review process spanning up to 10 days. The bill also provides additional funding to federal and local law enforcement to carry out those background checks and keep accurate criminal and mental health records.

One other thing the measure would do is clarify and expand the definition of a “federally licensed firearms dealer.” That’s important because current federal law only requires that licensed gun dealers conduct background checks when someone attempts to buy a gun. However, unlicensed sellers, such as people who sell guns online or at gun shows, don’t have to conduct background checks.

Finally, the package creates new federal criminal offenses for interstate gun trafficking and making straw purchases, meaning someone buying a gun on behalf of someone else, but telling the seller that they’ll be the owner of the gun. Though straw purchases are currently illegal under federal law, the idea is that the new offense categories will give prosecutors more tools to target criminals.

The bill has a few critical omissions

President Joe Biden, Democrats involved in the Senate negotiations, and gun control advocates have all said that the bill doesn’t go as far as they would like.

In a national address last month following the Uvalde shooting, Biden advocated for a ban on assault weapons and high-capacity magazines, raising the age to be able to buy a gun from 18 to 21, universal background checks, and allowing gun manufacturers to be sued if their weapons are used in violence.

None of those measures were adopted in the final version of the bill. But it’s been received as an important, incremental step towards further progress on gun control and a rare demonstration of bipartisanship on a hot-button issue that has stoked cultural divides.

Murphy said in a press conference earlier this month that he would have rather just raised the minimum age to purchase a gun to 21 and implemented universal background checks. But Senate Democrats met Republicans in the middle by enhancing background checks for young gun buyers and strengthening requirements for federally licensed dealers to conduct background checks.

“This bill doesn’t do everything. This bill will not end the epidemic of gun violence overnight. But it is substantial. It is significant. It will save lives, and it will provide us the momentum to be able to make further changes. That’s why I describe this as a breakthrough moment,” he added.

What happens now

The bill is expected to pass the Democrat-controlled House before Congress breaks for a two-week July 4th recess at the close of business this week, though it’s possible that the vote might not happen until the weekend. Biden has said that he intends to sign it once it reaches his desk.

But that won’t happen without protest from the House Republican caucus. Unlike Senate Minority Leader Mitch McConnell (R-KY), who supported the bill, all three House Republican leaders — House Minority Leader Kevin McCarthy of California, House Minority Whip Steve Scalise, and House GOP conference Chairwoman Elise Stefanik — have rebuked it.

At least some House Republicans, however, have announced that they intend to vote for the bill, including Rep. Tony Gonzales, who represents Uvalde.

“As a Congressman it’s my duty to pass laws that never infringe on the Constitution while protecting the lives of the innocent,” he tweeted on Wednesday.

It’s not clear, however, whether the bill might face legal challenges under the Supreme Court’s Thursday decision in New York State Rifle & Pistol Association v. Bruen, which, as my colleague Ian Millhiser writes, has put “vast swaths of American gun laws … in terrible danger.”

The court created a whole new framework for evaluating gun control laws that purports to be based on the text of the Constitution, as well as the history of English and early American gun laws. That framework could jeopardize a number of provisions in the Senate bill, including modern inventions like red flag laws and protections for victims of domestic violence.

That means that while it marks major progress, at least some of the bill could be vulnerable to legal challenges from pro-gun groups and states.