Sen. Tim Kaine (D-Va.) said describing the gun measure as a first step “accurately reflects people’s sincere hopes, and often success builds on success.” But he cautioned that “my read of the room here is, if we do this, we’ve got a lot of other issues that are on the table right now. And it’ll probably be a while before we return to anything in the gun safety space.”

Two months ago, everyone would have scoffed at the notion that the Senate could advance a bipartisan bill on one of the most polarizing subjects in American politics. Yet the final product also highlighted the stiff headwinds hindering support for broader proposals like raising the minimum age for assault weapons buys to 21.

And it’s not going to get any easier to write gun bills in a chamber where most legislation needs some GOP votes. The House is likely to flip to Republican control this fall. Democrats don’t have the votes to weaken the filibuster. Not to mention that a guns deal viewed by many Democrats as a modest accommodation to the GOP is getting support from fewer than one-third of Senate Republicans.

Some Democrats are tired of hearing the party line that they will come back for more later.

“This almost fell apart three times over the weekend. We are barely getting this done. And so one of the things I struggle with is, this constant ‘it’s not enough!’ and ‘we’ll get more later’ is just rank bullshit,” said one Democratic senator who requested anonymity to speak candidly. “For the foreseeable future, I think this will be the high-water mark.”

Republicans, meanwhile, said the forthcoming gun safety package is about as far as their party will go, especially considering that four of the 15 Republicans likely to back the bill will retire at the end of this Congress. Then there’s the political consequences of bucking the hard-core conservative faction of their own party as well as gun-rights groups like the National Rifle Association.

Sen. Mitt Romney (R-Utah), who supports the legislation, recalled suggesting to lead negotiators that they should include raising the minimum age to purchase assault weapons in their framework. They told him it wouldn’t get 60 votes.

“I predict [Democrats] will not be able to do more because we’ll barely get by with the Republicans they need to get this done,” the Utah Republican said. “So if they want to do something more than this, they’re not going to get 10” Republicans.

Members on both sides of the aisle acknowledge that the dynamics surrounding the previously elusive deal on guns changed after a gunman killed 19 children and two teachers in Uvalde at the end of May. Republicans saw Democrats as more willing to meet them in the middle on certain policy areas, like background checks. Democrats, meanwhile, saw a shift in some GOP senators’ openness to gun safety legislation.

For Sen. Chris Murphy (D-Conn.), the lead Democratic negotiator, the bipartisan compromise indicates that more gun safety legislation could be within reach.

“My theory has always been that once Republicans voted for gun safety measures they would find out that the sky doesn’t fall,” Murphy said. “We’ll have to see how this plays out for the Republicans. I think Republicans who vote for this will find a lot of new support back home that they didn’t previously count on, and I think they will find that the groups who were against this can’t really do much damage.”

Additionally, the effectiveness of the bipartisan gun safety package could heavily influence the likelihood of subsequent legislation. The bill provides grants for states to implement so-called red flag laws or other crisis intervention programs and closes what’s known as the “boyfriend loophole” by broadening firearm restrictions for domestic abusers. In addition, the legislation provides new spending for mental health and school security.

Republicans who support the legislation dismissed Democratic suggestions that it’s a first step in a more lengthy series of gun proposals, a line that tends to exacerbate fears among GOP base voters who worry any restrictions on gun ownership will become a slippery slope.

“They shouldn’t say that,” said Sen. Joni Ernst (R-Iowa), who voted to advance the package. “Because this is the effort that is going to get over the finish line. … All of these things are steps in the right direction. So let’s get it into place … and let’s see the results.”

The Senate’s expected passage of the bipartisan gun safety package comes after a series of failed attempts to curb gun violence. Most Republicans blocked a 2013 bill to expand background checks after the Sandy Hook school shooting. Negotiations in 2019 after back-to-back shootings in El Paso, Texas and Dayton, Ohio, fell apart as former President Donald Trump lost interest amid the House impeachment inquiry. The Senate did, in 2018, pass narrow legislation to improve reporting from federal agencies and states to the National Instant Criminal Background Check System.

That bill was written by Murphy and Sen. John Cornyn (R-Texas), the lead negotiators on this year’s gun safety package.

“We’ve tried to include in this everything that we could think of that might possibly have bipartisan support,” Cornyn said, describing how they approached negotiations this time around.

Cornyn didn’t rule out the possibility of revisiting the issue if circumstances require it. And senators in both parties suggested that additional congressional action will likely depend on the circumstances surrounding future tragedies.

That would require defying the political odds for a second time. So when will Congress act again on guns?

Senate Majority Whip Dick Durbin (D-Ill.) put it this way: “After waiting 30 years, I’m not ready to say.”