Senate Minority Leader Chuck Schumer is drawing a line in the sand: Democrats won’t vote for any replacement for FBI Director James Comey until a special prosecutor is chosen to investigate President Trump’s ties to Russia.

“We will have to discuss it as a caucus, but I would support that move, because who the FBI director is is related to who the special prosecutor is,” Schumer told CNN on Sunday. “To have that special prosecutor, people would breathe a sigh of relief, because then there would be a real independent person overlooking the FBI director.”

There’s just one problem with Schumer’s newfound spine: Republicans can easily snap it.

Because of a rule change in 2013 pushed through by Democrats, it will take just 51 votes for Senate Majority Leader Mitch McConnell to approve whomever Trump taps to replace Comey. Even if executed, Schumer’s (tentative) promise to have Senate Democrats vote against the next FBI director will do nothing to slow down the political opposition.

But that doesn’t mean Democrats have no option to try to force Senate Republicans to get Trump to appoint a special prosecutor. The reality is that, so far, the resistance’s allies in Congress have avoided taking it.

Activists want Democrats to shut down — or at least slow down — Senate business over the Comey firing

Left-wing activists have begun demanding that Senate Democrats do more than take the symbolically significant — but practically meaningless — position of voting against the replacement FBI director.

Instead, they’ve demanded that Democrats be willing to effectively shut down the Senate, triggering their “nuclear option” by withholding consent from the normal operations of the upper chamber.

Here’s how Senate Democrats’ “nuclear option” over Comey would work: Unlike the House of Representatives, the Senate operates under what are called “unanimous consent” agreements. If Senate Democrats withhold their consent, the routine functioning of the body — from committee hearings to routine floor votes — could grind to an immediate halt.

For instance, Senate Democrats could block McConnell on hundreds of decisions that are normally approved by unanimous consent without second thought — things like when the Senate will meet, minor and uncontroversial tweaks to legislation that don’t get written about in the press, and low-level presidential appointments that require Senate confirmation.

“It would stop everything in the Senate and effectively shut it down,” said Josh Huder, a congressional scholar at Georgetown University’s Government Affairs Institute. “If they go down this road, things could get pretty slow and ugly in the Senate.”

This is the path that leading progressive organizations like MoveOn.org, CREDO, Indivisible, and the Progressive Change Campaign Committee have demanded that Senate Democrats take.

"There's no reason Donald Trump should be able to confirm nominees or pass laws while smashing the rule of law to pieces," said Ben Wikler, Washington director of MoveOn.org. "This is an ‘in case of emergency, break the glass’ moment. Democrats should shut down the Senate until a special prosecutor is appointed.”

Democrats are set to consider the nuclear option this week

It’s not like Democrats aren’t aware of this strategy. In interviews, some said that while they haven’t embraced it yet, they’re strongly considering it depending on how Republicans react to Comey’s ouster.

For now, they’re seeing the more dramatic measure as a bridge too far. "I hope it doesn’t get there,” Sen. Dick Durbin, the No. 2 Democrat, said in an interview on Wednesday. “I’m hoping for a bipartisan approach to this. But let’s wait and see.”

Other Democrats sounded the same note. “I don’t think people will make a rash judgment about the right approach, but there is absolutely a consensus that we need to do whatever we can do [to get] an independent investigation,” Colorado Sen. Michael Bennet said.

Asked if Democrats should withhold unanimous consent, Pennsylvania Sen. Bob Casey noted that congressional Republicans would be needed for the formation of any bipartisan select committee.

“I think it’s got to be bipartisan — we have a lot of work to do,” he said. “So we haven’t made a decision on that.”

But even as McConnell dismisses calls for an independent investigation, Senate Democrats haven’t reacted by using all of their leverage. Two aides for Democratic senators told Vox Monday morning that they expected the proposal to come up at the party’s weekly caucus meeting on Tuesday.