On Monday evening, something exceptional happened in the Senate: Lawmakers confirmed a Circuit Court judge nominated by President Barack Obama. Luis Felipe Restrepo of Pennsylvania became only the second Circuit Court judge approved in the past year, and the 12th federal judge overall, an approval rate slower than any time since 1969.

Now, conservatives are demanding that Restrepo — who had a critical booster in GOP Sen. Pat Toomey of Pennsylvania — be the last Obama nominee confirmed before the president leaves office.

On Monday evening, the lobbying outfit Heritage Action called for an end to judicial confirmations during Obama’s final year, and on Tuesday it will call for an end to all confirmations except for those necessary to national security. The high-profile conservative group joined previous calls by Sen. Ted Cruz (R-Texas) and other senators to block Obama from filling any further vacancies, most notably, the federal courts, which could decide key parts of his legacy in the years and decades ahead.

So far, Majority Leader Mitch McConnell (R-Ky.) isn’t planning on a full blockade: He’s already agreed with Democrats to approve four more federal judges by the end of February. Still, that won’t make much of a dent in the backlog of 30 lifetime judicial nominees still awaiting confirmation

Beyond the four already slated for votes, Senate Majority Whip John Cornyn (R-Texas) said the nominee pipeline isn’t quite entirely closed.

“There is a point at which, traditionally, no additional judicial nominees are considered until the election,” Cornyn said. “There’s no formal rule or plan to my knowledge” to begin a cutoff now.

But McConnell has been taking his time on Obama’s nominations since Republicans took over a year ago, and there’s little reason to think the pace will pick up in 2016.

Blocking nominations has often been a unifying objective for McConnell’s conference, particularly after Democrats under then-Senate Majority Leader Harry Reid (D-Nev.) jammed through more than 100 judges when they last controlled the chamber. In retaliation, McConnell is setting a new low for confirming presidential nominees: In 2015, the Senate confirmed 173 total civilian nominees, according to the Congressional Research Service, about 100 fewer than were confirmed in 2007 when a Democratic Senate took over during the last two years of George W. Bush’s presidency.

That’s just fine with Heritage Action. As the House and Senate GOP prepare to head to Baltimore for a joint retreat on Wednesday, the group is circulating a document calling for a near-complete stop to the confirmation process.

“Given the Obama administration’s disregard for Congress’s role in our constitutional system of government, the Senate should refuse to confirm the president’s nominees unless those nominees are directly related to our national security,” Heritage will ask of Republicans in guidance distributed to members. The directive was first shared with Politico.

Meanwhile, the administration has launched a concerted push to confirm national security nominees, like a new ambassador to Mexico and a terrorism finance overseer, with Secretary of State John Kerry calling Reid this month to press his case. In an interview, Reid said there’s little he can do.

But the courts will battle over Obama’s legacy for years, particularly given his push on executive actions on guns, immigration and the environment, giving judicial confirmations more long-term impact than confirmations to fill out the last year of an administration. Plus, at this point, Obama can use workarounds like interim appointments to staff some of the executive branch, like the Education Department’s top job.

And McConnell is taking his nomination blockade a step further on judges. Since 1993, the Senate has never confirmed fewer than 50 judges during a two-year session of Congress, according to CRS, but if McConnell continues his current confirmation pace he may barely scratch half that.

Historically, Senate leaders slow lifetime judicial confirmations dramatically during the last year of a presidency, in a nod to precedent of the “[Strom] Thurmond Rule,” which calls for the end of judicial confirmations during the last year of a presidency and as the election approaches. Both parties have abided by the Thurmond Rule during the last decade’s pitched confirmation wars, and McConnell actually began employing the rule in 2012 as the GOP made a run at ousting Obama.

“Other than [me] complaining about it, it’s up to [McConnell]. We’ve tried,” Reid said in an interview on Monday. “The Thurmond Rule has been employed since they took the majority. That was a year ago.”

At a POLITICO event in December, McConnell said there “isn’t any particular official or unofficial” cutoff date for judicial confirmations and said Obama has enjoyed hundreds of confirmations over his presidency. Yet GOP senators have privately discussed when to begin cutting off judges this year, though they have not proposed any strategy as aggressive as Heritage Action.

“It’s almost always the case that that happens at some point. So I’m sure at some point we’ll invoke the [Patrick] Leahy-Thurmond rule, which typically involves at a minimum halting confirmation on any circuit court and Supreme Court nominees that are going to be made,” said Sen. Mike Lee (R-Utah), who chairs the conservative Republican Steering Committee.

Cruz, for example, recommended nearly a year ago that McConnell allow no confirmations for Obama as long as he was pushing executive action on immigration. Obama is still pushing, and dozens of nominees have been confirmed since.

With Restrepo’s confirmation, there are now 30 lifetime judicial nominations, mostly district court judges, awaiting either confirmation or committee votes in the Senate. But that reveals only part of the picture: The federal government cites nearly 80 total vacancies on the federal courts and 33 total judicial emergencieswhere courts are understaffed and overworked.

According to the liberal group People for the American Way, that’s about half the number of such emergencies at this time during 2008, the last year of George W. Bush’s presidency. Yet as noted by Judiciary Chairman Chuck Grassley (R-Iowa) on Monday, Obama still has seen more judicial nominees confirmed overall than Bush.

“[Restrepo] will be the 319th judicial nominee confirmed during President Obama’s presidency. By comparison, at this time in 2008, the beginning of President Bush’s last year in office, the Senate had confirmed only 297 judicial nominees,” Grassley said.

One factor that could help Obama in his last year: Home-state politics. Toomey was hammered for months as Restrepo’s nomination stalled, and he now has four Pennsylvania district court nominees moving through the confirmation process. It may upset the conservative base, but a few confirmations could be helpful to Toomey, who faces a tough path to reelection this fall.

Conservatives: No more Obama nominees