“If you’re too dangerous to board a plane, you’re too dangerous to buy a gun.”

That’s the bumper-sticker-simple premise Senator Diane Feinstein used to sum up legislation she has co-sponsored to block those on the consolidated terror watch list from buying guns. The California Democrat introduced her bill, the Denying Firearms and Explosives to Dangerous Terrorists Act, in February, around the same time that Republican Representative Peter King proposed a similar bill in the House. But the so-called “terror gap” didn’t develop political momentum until ISIS-affiliated terrorists shot and killed more than 100 people in Paris last month. In the wake of the San Bernardino attacks, Democrats have redoubled their efforts to close the loophole, in the process inverted the usual roles in in gun reform debates, putting Republicans on the defensive by linking the issue to national security.

In response, Senate Republicans offered their own solution when Democrats attempted to attach Feinstein’s plan to a Obamacare repeal bill the day after the San Bernardino shooting. Both sides’ terror gap fixes fell short during that skirmish — but the issue is all but certain to stay on the agenda well into 2016, especially as presidential candidates are forced to stake out positions on the dueling proposals. Meanwhile, some governors are taking matters into their own hands, presenting a third venue for debate.

It’s all a lot to keep straight. Below, a guide to whose proposal does what — and the larger aims of each.

The Feinstein plan

Feinstein’s bill calls on the Justice Department to check would be gun buyers against the government’s consolidated terror watch list — which is much larger than the “no fly” list, including a reported 800,000 names, of whom an estimated 40,000 are Americans. (The “no fly” list is a much smaller subset, containing approximately 6,400 Americans out of 64,000 names in all.) The bill does not require the Justice Department to block the sale when a background check returns a match, though it does give the Attorney General that authority. Republicans oppose the measure on the grounds it would strip those on the watch list of their constitutional right to a gun without due process.

Democrats have been open about the political aims of forcing votes on smaller-bore gun measures like the terror gap as part of a strategy to turn the larger issue to their advantage. “There are a good number of our Republican colleagues dreading these two votes,” New York Senator Chuck Schumer told reporter last week. “Dreading them.” New Hampshire’s Kelly Ayotte, up for re-election next November, is one of those: two days after voting no on Feinstein’s amendment, she sought to preempt future political attacks, tweeting that said she favored banning those on the no-fly list from purchasing guns, provided there was “due process for Americans who are wrongfully on the list.”

The Republican alternative

Introduced by Texan John Cornyn, the Senate Majority Whip and a frequent author of pro-gun legislation, the Republican plan allows the government to block a firearms sale only when it can provide sufficient proof that the prospective buyer “has committed, or will commit, an act of terrorism.” When a gun shopper on the terror watch list triggers that process, the Justice Department would have no more than 72 hours to assemble its case and secure what’s called an “emergency judicial motion” by presenting a judge with probable cause. If the Justice Department fails to do that, the purchase would go through.

The Cornyn proposal employs a higher burden of proof than the terror watch list itself, which is a tool for ongoing intelligence gathering and investigations. Senate Minority Leader Harry Reid calling the plan “dangerous” and “ridiculous.” Neither Feinstein or Cornyn’s offices returned requests for comment.

The state option

Just as states have enacted a flurry of new gun laws in recent years, so have they presented a separate forum for addressing “the terror gap.” In 2013, New Jersey Governor (and now Republican presidential hopeful) Chris Christie signed a law that bans those on the terrorist watch list from buying guns in the Garden State. When the issue rose to new prominence this fall, he initially stopped short of imposing his approach on his fellow governors, telling CNN’s Jake Tapper that he believed that the matter is best left up to individual states. Following the San Bernardino attack, though, he modified his position, saying that he “doesn’t mind” federal action on the subject.

In recent days, Democratic governors in two traditionally left-leaning states have expressed interest in implementing similar bans. Connecticut’s Dannel Malloy said he would sign an executive order banning individuals on the watch list (as well as suspected gang members) from purchasing guns in his state. New York’s Andrew Cuomo said over the weekend that he’d like to follow suit.

To implement such policies, both states would need to a way to access the classified terror watch list database. Malloy has said his office is in negotiations with the White House to make that happen. New Jersey police officials told the Connecticut Mirror that while they don’t have a copy of the terrorist watch list, they are able to check names against the list during the state’s usual gun background check procedure. “We do have access to that data,” a police captain said.