Four months after the Sandy Hook massacre, the Senate voted today to proceed with debate over the most ambitious gun legislation since the 1990s.

By a vote of 68-31, the Senate averted a threatened Republican filibuster and opened up what is almost certain to be weeks of fierce discussion over a range of proposals intended to curb gun violence.

Today's vote is only a small win for Democrats, as final passage of any gun bill is still very much in doubt. Many Republicans have vowed to defeat the legislation or block it from reaching a final vote, and the NRA has said it will score an ensuing cloture vote as part of the gun-right's group's influential lawmaker grades.

Here, five key takeaways from today's vote:

1. The filibuster was busted
Sixteen Republicans crossed the aisle and voted for cloture with Democrats, negating a filibuster attempt led by three Tea Party conservatives: Sen. Rand Paul (R-Ky.), Sen. Mike Lee (Utah.), and Sen. Ted Cruz (Texas.) Twenty-nine Republicans voted against the measure, including Minority Leader Mitch McConnell (Ky.), who said Thursday that "the government should not punish or harass law-abiding citizens in the exercise of their Second Amendment rights." 

Until this week, it remained unclear if Republicans had the numbers to down the procedural vote. Thirteen GOP senators had already sent a letter to Reid threatening a filibuster.  

But as more and more Republicans publicly said this week that they would not join that filibuster attempt — including prominent faces like Sen. John McCain (R-Ariz.) and Sen. Lindsay Graham (R-S.C.) — Senate Majority Leader Harry Reid (D-Nev.) filed cloture Tuesday night, setting up Thursday's showdown vote.

2. But it may be too soon to celebrate
"The hard work starts now," Reid said after the vote, acknowledging that the bill is still far from becoming law. Though Democrats won this first round, it's but the first in a multi-step process that will only get tougher as legislation inches along. 

"The vote, while a short-term victory for gun-control advocates, in no way presages passage of new gun laws," says The New York Times' Jennifer Steinhauer. "The impending bill will again need 60 votes to end the debate after consideration of contentious amendments offered by both supporters and opponents of new laws."

If the bill clears that second huge hurdle — and given that it narrowly passed today, that seems like a daunting task — it would then still need to receive 51 supporters in a final round of voting to become law. Sen. Max Baucus (D-Mont.), who voted today to begin debate, has already indicated he'll vote against a final bill, and other Democrats from swing states are expected to join him. 

Opponents could also stall a vote by offering amendment after amendment, attempting to weaken support by extending the process and watering down the legislation. According to Politico's John Bresnahan, "Republicans are expected to offer dozens — if not hundreds — of amendments and string out debate over the next few weeks."

Should that tactic fail, opponents could also try to tack a "poison pill" amendment to the bill, making it politically unfeasible and guaranteeing its failure. If a bill somehow finds its way through that minefield and wins final passage in the Senate, it would face even longer odds in the Republican-controlled House. 

3. Some Democrats defected
Democrats were not fully unified in their support for moving on to debate the bill. Two red-state Democratic senators who face potentially bruising re-election fights next year — Alaska's  Mark Begich and Arkansas' Mark Pryor — broke ranks, with Begich saying he wanted to see the bill's final contents before moving forward.

"I think people should have the opportunity to vote if they know what they're voting on," Begich told Alaska's Daily News-Miner. "I might be one of those that, at the end of the day, doesn't vote for cloture, because anyone can talk about amendments, but we haven't seen one of them yet." 

4. It was a 'small victory' for Newtown
Families from Newtown, Conn., were on hand for the vote, as were a number of gun-control activists. In the preceding weeks, they'd pressed the Senate to simply hold any vote, period, with a group called the Newtown Action Alliance declaring on its Facebook page that "Newtown deserves a vote." Reid echoed that sentiment Tuesday, saying it would be a "real slap in the face" to gun-control advocates for the Senate to not hold a vote.

"Congrats for a small victory," the Newtown Action Alliance wrote Thursday, celebrating the procedural win. "The filibuster has been busted!" 

5. Joe Manchin was the key dealmaker
The West Virginia Democrat has suddenly found himself at the center of bipartisan talks. Manchin, with his A rating from the NRA and his willingness to buck the party on some issues, was seen as a critical consensus-builder — and he has so far delivered. 

On Wednesday, Manchin announced a comprise he'd reached with Sen. Pat Toomey (R-Pa.) — another A-rated senator, per the NRA — on universal background checks. Expanding background checks has become Democrats' top goal since they abandoned plans for an assault weapons ban. On Thursday, Reid said the Manchin-Toomey proposal would be the first amendment brought up for consideration.

"Before Wednesday, Sen. Joe Manchin III was not known for crafting complicated legislation. He was known for shooting it," says The Washington Post's Ed O'Keefe, referring to a 2010 Manchin campaign ad that showed him literally shooting a Democratic-backed cap and trade bill.

As with the gun bill as a whole though, the background check provision faces a tough road ahead. The powerful NRA opposes it, and several lawmakers have already threatened to weaken the measure, or block it wholesale.