Here's how politically tricky the gun-control debate has become: A Republican-controlled Congress might soon vote on a bill to strengthen gun-control laws in the wake of the Florida shooting, and it's the Democrats who aren't happy about it.

Even though one of their own is co-sponsoring the Fix NICS Act, which would punish federal agencies that don't submit criminal records to the national criminal background check system for firearms, Senate Democrats have spent their first few days back in Congress this week dissing the bill.

“What will prevent future tragedy? Comprehensive background checks will. The Fix NICS bill will not,” Senate Minority Leader Charles E. Schumer (D-N.Y.) said Tuesday on the Senate floor. “Let’s not set our sights too narrow or squander this moment.”

It's not that Democrats don't want to patch up what both sides say are obvious holes in the background-check system; it's that they think this is a small step to reinforce an existing law rather than expand it. And if they support it, that might be the end of gun control reforms in this Congress, since Republicans will be reluctant to act on much else.

This leaves Democrats toying with opposing the one gun-control bill that has a realistic shot of passing Congress right now, one championed by their most vocal gun-control advocate, Sen. Chris Murphy (D-Conn.). It's a weird look, for sure.

Murphy doesn't want his own bill brought up for a vote without a guarantee from Republicans to allow votes on other Democratic priorities, like universal background checks. “If we were only to debate the Fix NICS Act,” Murphy told reporters Tuesday, “we would be slamming the door in the face of all these kids who are demanding change.”

That's a sharp turn from what Murphy said in November, calling his bill the most important piece of bipartisan gun-control legislation since the Senate voted on (and didn't pass) a universal background check proposal after the Sandy Hook shooting in Newtown, Conn.

There is no such bill circulating after the massacre at a Parkland, Fla., high school. The lack of viable gun-control legislation in Congress right now is also precisely why Democrats feel pressured to resist this incremental step.

Democrats are fully aware that this vote is their only point of leverage in the debate, so they've got to play hardball to try to extract as much as they can from it. The Post's Ed O'Keefe reports they're also working with gun-control groups to find a way to politicize this whole issue to their advantage in November's midterm elections.

It's difficult to see another gun-control measure coming up for a vote right now. There is a bipartisan bill to raise the age limit on purchasing rifles circulating in the Senate, but President Trump has backed off that proposal in the past few days, severely stalling its momentum. The other potential area of compromise — on whether to ban bump stocks used in the Las Vegas shooting — is now mostly in the hands of the Trump administration, not Congress.

Left with this one piece of legislation, Senate Democrats' strategy appears to go like this: By openly contemplating holding out their votes to move forward on this modest bill, they are hoping to force Republicans to allow a debate and vote on other gun control measures — like universal background checks, or banning assault weapons.

That doesn't mean that those gun-control measures will actually pass. In fact, in a Congress that requires 60 votes to do anything major and with only 49 Democrats, more significant gun-control legislation almost certainly won’t pass the Senate, let alone the more conservative House.

But at the very least, Democrats can say they got a Republican-controlled Congress to vote on gun control. They might even win over a GOP convert or two, as after the 2016 Orlando shooting when then-Sen. Kelly Ayotte (R-N.H.) changed her vote in favor of Democrats' proposal to prevent suspected terrorists on watch lists from buying guns. (That proposal and other Republican ones failed.)

Gun-control advocates measure their victories extremely incrementally right now. After Parkland, some Senate Democrats have lamented not acting on gun control when they had control of Congress and the White House in 2009 and 2010. But they didn't have the votes then, even when Democrats had a filibuster-proof majority in the Senate.

So getting a Republican-controlled Senate to just allow votes on gun-control measures would be no small thing politically. And Democrats probably do want to use this moment, if they can seize it, to identify significant converts.

Sen. Marco Rubio (R-Fla.) said he'd support raising the purchasing limit for assault rifles from 18 to 21 and that he'd consider regulating high-capacity magazines. In the House of Representatives, Rep. Brian Mast (R-Fla.) said he'll support an assault-weapons ban. Even one or two Republican votes on those measures would be a seismic break in the politically hardened gun debate.

“We have Republicans expressing support for some these measures that never expressed support before,” Murphy said Tuesday. “That begs us to have a debate on the floor, so that we can find out what measures can pass and what measures cannot pass.”

But to get that, Democrats also risk holding up one of their own bills. Such is the strange politics of gun control right now, and the delicate situation Democrats are in.