RICHMOND — Gov. Ralph Northam's assault weapons bill was in trouble — not from Republicans in the newly blue legislature, but from a handful of fellow Democrats in the Senate.

The day before the General Assembly gaveled into session last month, in a closed-door caucus meeting, Sen. Chap Petersen (D-Fairfax City) and a few rural lawmakers said they wouldn’t support all eight pieces of Northam’s gun-control agenda.

Specific details of some measures worried the senators. For Petersen at least, the main concern was the sheer number of bills. His limit, he said that day, was four.

“It’s just piling on,” he said in an interview last week, after he and three other Democrats joined with Republicans to kill the ban on future sales of assault weapons in committee. “You can’t discount people that were raised and grew up in this state and have their own traditions. You can’t just suddenly kick them to the curb.”

Virginia’s Capitol is in the midst of a revolution, with the House, Senate and Executive Mansion under Democratic control for the first time in a quarter-century. Legislation that routinely died with Republicans in charge has flown out of both chambers, including measures to raise the minimum wage, shift to clean energy, decriminalize marijuana, ban anti-LGBT discrimination and let localities remove Confederate monuments.

But there are limits to how far some Democrats want to go, even on gun control — the party’s marquee issue in the November elections.

The Senate — whose members are older, more tenured and less racially diverse — has taken less liberal positions than the House in many areas, including labor and immigration. Still, the defections on the assault weapons bill infuriated advocates and House Democrats given the issue’s prominence in fall campaigns.

“There’s almost 30 years of pent-up policy waiting to get passed,” fumed Lori Haas, who has been lobbying for tighter gun laws since her daughter was wounded in the Virginia Tech mass shooting in 2007. “And the notion that incremental is somehow the way to go . . . it’s ridiculous.”

Petersen said such complaints miss the big picture: Both chambers have passed a host of gun-control bills, including those that require background checks on all gun sales, cap handgun pur­chases at one per month and create a “red flag” law allowing authorities to temporarily seize weapons from people deemed a threat.

“We’ve passed more bills on gun safety in the last 30 days than we’ve done in the last 30 years,” he said. “And by the same token, I like to be able to say, ‘You know, we did listen to the other side. We did dial a couple things back. We did say “no” to a couple people.’ ”

The bill’s failure could exacerbate House-Senate tensions — a day later, House Democrats killed Petersen’s bill to allow part-time law enforcement officers to buy their service weapons when they retire. But Democrats in the two chambers will have to find a way to work together if they are to iron out differences in every bill that hasn’t passed both chambers in identical form, gun measures included.

Gun control became a rallying cry for Democrats after last year’s mass shooting in Virginia Beach, especially after Republicans swiftly gaveled in and out of a special session on guns that Northam called in the aftermath, refusing to consider the governor’s eight gun-control bills.

All eight seemed headed for passage after Democrats won the House (55-45) and Senate (21-19). Gun owners were alarmed, particularly by the assault weapons bill. As originally proposed, it would have forced owners to give up certain legally purchased firearms.

Even after Northam promised a grandfather clause — banning future sales but allowing people to keep assault weapons they already owned — the uproar swelled.

More than 110 counties, cities and towns would eventually declare themselves Second Amendment “sanctuaries” where new gun laws would not be enforced. Tens of thousands, including militia groups from across the country, would flock to an annual gun rights rally that typically draws a few hundred to the Capitol.

On the eve of the legislature’s Jan. 8 opening day, Petersen and Democratic Sens. R. Creigh Deeds (Bath), John S. Edwards (Roanoke) and Lynwood W. Lewis Jr. (Accomack) told their caucus they would not support the assault weapons bill.

Deeds and Edwards said the legislation’s definition of “assault firearm” was imprecise. Lewis who was not on the committee that ultimately killed the bill said a ban on future sales would be ineffective given the “tens of thousands” already in private hands in Virginia.

“The sanctuary nonsense kind of got people spooked,” said Sen. Mamie E. Locke (D-Hampton), who supported the measure.

Northam had asked Sen. Adam P. Ebbin (D-Alexandria) to introduce his proposed ban in the Senate. It never materialized.

“I did spend a lot of time working on that,” Ebbin said. “However, I can also count votes and . . . I decided to focus on a few things that I thought might have a better chance.”

Senate Majority Leader Richard L. Saslaw (D-Fairfax) had submitted his own version in November but struck it a few days into session. That left the Senate with no assault weapons bill to consider — until the House version, proposed by Del. Mark H. Levine (D-Alexandria), squeaked out of that chamber hours ahead of the Feb. 11 “crossover” deadline.

The Senate Judiciary Committee docketed the bill right away, even before Northam’s seven other gun-control bills, which cleared the House nearly two weeks earlier and will be heard Monday. Northam, Public Safety Secretary Brian Moran and House Speaker Eileen Filler-Corn (D-Fairfax) spent the days ahead of last week’s meeting asking for more time to address objections.

“This was no surprise to anyone that we were going full steam ahead on these eight bills,” Moran said.

Last week, four of the nine Democrats on the Senate committee — Petersen, Deeds, Edwards and Scott A. Surovell (Fairfax) — sided with Republicans to reject the assault weapons bill for the year, sending it to the state’s Crime Commission for study. The vote was 10 to 5.

The only real surprise was Surovell, who wrote on his blog afterward that he does not support civilian ownership of assault weapons as someone who “lived through the 2002 D.C. sniper attacks while crouching in my car getting gas to avoid being shot.”

But Surovell, like the others, had issues with how the bill defined the weapons. He was concerned by a provision forcing owners to give up large-capacity magazines. Without a buyback program, which the bill lacked, the mandate could constitute an unconstitutional “taking” of property, he said.

Surovell said he believes those problems can eventually be worked out but said doing so would take more time than legislators can spare amid this year’s legislative avalanche.

“In a part-time legislature, there’s only so much oxygen in the room,” he said. “I was just voting to continue the discussion.”