If Hillary Clinton wins, conservatives have already devised a new litmus test for how truly anti-Clinton a Republican is: Will they commit to blocking any Clinton nominee to the Supreme Court?

Over the last year, preserving the Supreme Court has become the symbol by which Republicans have rationalized falling in line behind unpredictable, conservative poser Donald Trump. Evangelicals have ignored Trump’s crass comments about grabbing p***y in the name of Roe v. Wade. Sen. Ted Cruz (R-TX) won’t say the nominee’s name on the stump, but he’s quick to point out the importance of voting for the “Republican nominee” in order to preserve the balance of the court.

And slowly but surely, vowing to block Hillary Clinton from ever getting a nominee through the Senate if she is elected has become normalized.

What began as brash campaign rhetoric is now being adopted by the conservative base as the litmus test of what it means to be a Republican. Anything short of it could be construed as RINO territory.

Sen. John McCain (R-AZ) became one of the first lawmakers to reveal that thinking. During a radio program campaigning for Sen. Pat Toomey (R-PA), McCain said he promised “that we will be united against any Supreme Court nominee that Hillary Clinton, if she were president, would put up.” (Later his campaign clarified he’d look at their qualifications first before making a final decision on how to vote.)

In an interview with reporters, Sen. Ted Cruz (R-TX) pointed out last week there was precedent to have fewer than nine justices.

Sen. Richard Burr (R-NC), whose locked in a bitter re-election contest, said “if Hillary Clinton becomes president, I am going to do everything I can do to make sure four years from now, we still got an opening on the Supreme Court.”

It could all be chalked up as campaign trail bluster except that conservative outside groups are beginning to signal they’re ready to invest pressure on members who fall outside the party line,

The Hill reported last week that Dan Holler, a spokesman for Heritage Action, said it was “unacceptable” for Republicans to allow Clinton’s nominees to get through.

“You’ve seen John McCain and others talk about the need to not confirm any liberal nominated to the Supreme Court,” Holler said, according to the Hill. “That’s exactly the right position to have.”

Heritage Action told members in the briefing that it was going to take “an immense amount of willpower,” to follow through, but the message was clear that it is the preferred path if Clinton has a victory Tuesday.

There’s a real danger, of course, in overpromising on the trail and whipping up the base on something as important as the Supreme Court.

But, Republicans have repeated this perilous strategy before. The promises Republicans are making about the court are not so different than the far-flung and unkeepable promise they made to voters in 2010, then again in 2012 and 2014 that they would repeal President Barack Obama’s signature health care law.

Republicans knew political reality and they understood that a repeal of Obamacare was never going to happen with Obama in office. And yet, they kept on talking about it until their base was so strung out on red meat promises, frustrated and tired of being lied to that they nominated Donald Trump for president.

There are plenty of outcomes possible on Tuesday. Clinton could, of course, win with a Democratic majority in the Senate and the entire conversation about a full-out Republican blockade could be resolved with Democrats revising the filibuster rule. But, with key Senate races still close, it’s just as plausible that Republicans will hold the Senate in 2017 and Clinton will be forced to navigate a long and entrenched blockade of the Supreme Court.

Not every Republican is so bold to say outright say they’ll block Clinton’s nominees indefinitely. The chairman of the Senate Judiciary Committee, Chuck Grassley (R-IA), admitted the GOP “cannot stonewall forever.” But what would keep Republicans from establishing an impossibly high bar that Clinton could never deliver on?

On the trail, some Republicans have been more nuanced about how they’d consider Clinton’s nominations, but they are hardly saying they’d embrace anything short of a constitutional conservative.

“I can’t imagine voting for a Clinton nominee unless she would appoint somebody that actually … believes in the separation of powers as the Founders wrote into the Constitution, ” Sen. Rand Paul (R-KY) said during his debate, according to NPR.

Sen. Marco Rubio (R-FL) has made similar statements.

Not all Republicans are gonna pass this litmus test, however.

Sen. Jeff Flake (R-AZ) is pushing to actually just approve Obama’s nominee Merrick Garland in the lame duck session to avoid getting a more liberal nominee from Clinton in 2017. Sen. Johnny Isakson (R-GA) said if Clinton was elected he thought the Senate would confirm Garland, according to the Atlanta Journal Constitution. Isakson also said that in the future, he would “consider who [Clinton] nominates at the time she does and make a decision that’s right for the people of Georgia.”

A spokesman for Georgia Sen. David Perdue (R-GA) said in a statement that “as a member of the Judiciary Committee, [Perdue] wants to ensure we have a Supreme Court Justice who will uphold the Constitution, and he will examine each nominee independently based on their merits.”

And, in an interview with Politico, Sen. Jim Inhofe (R-OK), said he could support a candidate who was more moderate coming from Clinton.

But, now that Republican base voters have been told it’s possible to block any and all of Clinton’s Supreme Court nominees forever, it’s hard to believe they will accept anything short of it.