Originally Published: 17 APR 23 08:27 ET

Updated: 18 APR 23 11:13 ET

By Manu Raju and Lauren Fox, CNN

(CNN) -- Senate Republicans are prepared to block Democratic efforts to replace Sen. Dianne Feinstein on the powerful Judiciary committee, ratcheting up pressure on the 89-year-old California Democrat to resign or return quickly to allow President Joe Biden's judicial nominees to be confirmed.

Democrats would need 60 votes to replace Feinstein on the panel, but senior Republicans in leadership and on the committee made clear Monday that they would not give them the votes to do that. The result: At least 12 nominees — and maybe more — could be stalled if Feinstein does not return soon.

The stakes are high for Democrats, who could see key agenda items thwarted -- both on the committee and on the Senate floor -- if they are unable to replace Feinstein and the California Democrat does not return to Washington soon.

Many congressional Democrats have remained largely supportive of Feinstein's decision to remain in office while absent from the Capitol as she continues to recover from shingles. But Feinstein has faced calls to resign from two House Democrats, and if Democrats are not able to replace her on the committee that number could grow in the days ahead.

Senate Minority Leader Mitch McConnell outlined the GOP's opposition on the Senate floor on Tuesday.

"Senate Republicans will not take part in sidelining a temporary absent colleague off the committee just so Democrats can force through their very worst nominees," he said.

The comments were echoed by top Republicans, a clear sign Democrats lack the votes they need.

Sen. John Cornyn, a senior member on the Senate Judiciary Committee and close adviser to McConnell, told CNN that he opposes the effort to replace Feinstein on panel.

"I don't think Republicans can or should help President Biden's most controversial nominees," Cornyn said. "I support having Sen. Feinstein come back as soon as she can. But this effort to confirm controversial and in many instances largely unqualified nominees, I don't think you can expect any Republican cooperation."

Sen. Chuck Grassley — the 89-year-old Republican and senior committee member — contended the current situation has nothing to do with senatorial courtesy.

"I don't think senatorial courtesy will work to move liberal judges," he told CNN.

Senate GOP Whip John Thune suggested Democrats are using their request to remove Feinstein from her post as a way to put "pressure" on her to resign. "The Dems are sort of using this because they want pressure on her to resign and I think this gives them... sort of a lever to do that," he said.

Thune added that he thinks, based on the response so far from GOP members, that the request is certainly not going to be a "slam dunk" for Democrats.

Sen. Joni Ernst told reporters, "we're not going to help the Democrats with that" when asked if she'd back a resolution to temporarily replace Feinstein.

Republican Sens. Tom Cotton of Arkansas and Marsha Blackburn of Tennessee, both members of the committee, took to Twitter to express opposition.

"I will not go along with Chuck Schumer's plan to replace Senator Feinstein on the Judiciary Committee and pack the court with activist judges," Blackburn said on Monday.

"Republicans should not assist Democrats in confirming Joe Biden's most radical nominees to the courts," Cotton tweeted over the weekend.

Whether or not Democrats are able to replace Feinstein on the panel could have major implications on Biden's efforts to fill the judiciary and shake up the California Senate race.

That's because if Republicans deny Democrats the 60 votes needed to remove Feinstein from committee, as she has requested after being out for the past two months due to shingles, it will only intensify pressure on Feinstein to resign from the Senate. If she does, it could very well rattle the California Senate race given that Democratic Gov. Gavin Newsom has previously vowed to name a Black woman to the position — and it's unclear if that appointed senator may also compete for Feinstein's seat in 2024.

Schumer has said he will ask the Senate this week to make the change, but when he will do so is subject to tedious negotiations on the front end to see what is possible before he brings it to the floor.

There is a reason that while Feinstein has been gone, the Senate Judiciary Committee has had to repeatedly postpone votes on judges. Without Feinstein, the committee is tied. Under the power-sharing agreement in the last Congress, which had a 50-50 Senate, there was a provision that allowed for a tied nominee to be discharged from committee and put on the floor. That rule is no longer in place, according to an aide on the committee.

So unless a judge has bipartisan support -- and some of them in the pipeline still do -- the nominee fails in committee and doesn't come to the floor.

Senate Judiciary Chairman Dick Durbin stopped short on Monday of calling on Feinstein to resign, saying he hopes that Republicans will help to temporarily replace her on the committee and recognize that "the rain can fall on both sides of the road."

"The Republicans ought to think a little bit about what this means. Tomorrow, they could be facing exactly the same thing," Durbin said.

The issue has served as a reminder that the US Senate's average age is 65 years old, with many members older than that. The reality is that Feinstein is not the first, and will not be the last, to have an extended absence from the body. Senators are cognizant that launching a fight today over this one absence could come back to haunt the other party in the future.

When asked about the timeline for trying to replace Feinstein, Durbin punted, saying the process will "be in Sen. Schumer's hands."

After decades of service, Feinstein still has not returned to the Senate after announcing in early March she had shingles. Questions have since mounted about her health, when and if she will return to the US Senate, and how the Senate Judiciary Committee, which has a narrow, one-vote margin, would continue to implement the Biden administration's judicial legacy in the wake of her absence. The importance of the lower courts has been especially highlighted by the recent fight over abortion rights.

Tensions came to a head last week when two Democratic House members -- Ro Khanna of California and Dean Phillips of Minnesota -- called on Feinstein to resign, an unusual breach in precedent. Hours later, Feinstein issued a public statement and requested to be pulled, albeit temporarily, from a committee where she cemented a decades-long legacy.

Feinstein serves on several other committees but is not asking to be temporarily replaced there.