Many on the left had quietly hoped that Justice Stephen Breyer would retire in 2021, opening up a seat on the Supreme Court for President Biden to fill — but now some are waging a public campaign to pressure the liberal stalwart to step down. 

The calls come in the wake of a speech Breyer gave to Harvard Law School students and alumni earlier this week when he warned that court packing – a term for adding seats to the Supreme Court to change its political makeup – could harm the rule of law in the U.S.

"Proposals have been recently made to increase the number of Supreme Court justices. I'm sure that others will discuss related political arguments," he said. "This lecture reflects my own effort to be certain that those who are going to debate these questions ... also consider an important institutional point. Consider it. Namely, how would court packing reflect and affect the rule of law itself?"

Breyer said that he aimed "to make those whose initial instincts may favor important structural change, or other similar institutional changes, such as forms of court packing, think long and hard before they embody those changes in law." 

LIBERAL JUSTICE STEPHEN BREYER WARNS AGAINST COURT-PACKING

Some on the left reacted negatively to Breyer's comments. Demand Justice, a liberal group dedicated to making the federal courts more left-leaning, responded by doubling down on its calls to "Expand the Supreme Court."

Days later, Demand Justice is further lashing out at Breyer, who for decades has sided with left-leaning litigants more often than not. 

"Breyer, retire," a billboard truck paid for by Demand Justice, that was driving around Capitol Hill Friday, reads. "Don't risk your legacy." 

Another side of the truck reads, "It's time for Black woman Supreme Court justice. There's no time to waste." 

The group elaborated in a tweet. 

"We can't afford to risk Democrats losing control of the Senate before President Biden can follow through on his promise to nominate the first Black woman Supreme Court justice," Demand Justice tweeted. "It's time for Justice Breyer to announce his retirement."

The push comes as Biden announced a commission to study possible reforms to the Supreme Court, including court-packing. He gave the 36-member group 180 days from its first public meeting to produce a report on its findings. Biden announced during the presidential campaign that he would create such a commission in a "60 Minutes" interview. 

"It's not about court packing," Biden. "There's a number of other things that our constitutional scholars have debated, and I've looked to see what recommendations that commission might make. ... There's a number of alternatives that go well beyond packing."

 Some on the right panned Demand Justices' efforts to get Breyer to step down.

"The left-wing dark money groups," Judicial Crisis Network President Carrie Severino said, "are clearly frustrated with Justice Breyer. They thought they paid for court-packing when they elected Joe Biden and the Senate Democrats, but Breyer is not helping them to get it done."

Doug Andres, the press secretary for Senate Minority Leader Mitch McConnell, R-Ky., chose to make fun of the Demand Justice effort. 

""Wait, they have a BILLBOARD TRUCK?! Checkmate. I shall retire now.' - Justice Breyer," he tweeted. 

"I'm sure Supreme Court Justice Stephen Breyer, who's served for almost 30 years, is shaking in his boots at an online petition from Demand Justice," added National Republican Senatorial Committee Communications Director Chris Hartline. 

Mike Davis, the president of the conservative Article III Project, pointed to the unsuccessful liberal campaign during the Obama administration to get late Justice Ruth Bader Ginsburg to retire. 

White House press secretary Jen Psaki – who used to work for Demand Justice – did not call on liberals to lay off their pressure campaign against Breyer when asked on Friday. She did say that it is up to Breyer to decide when he leaves the bench. 

President Biden looks on during his visit to Smith Flooring, Inc., on March 16, 2021, in Chester, Pennsylvania. 

President Biden looks on during his visit to Smith Flooring, Inc., on March 16, 2021, in Chester, Pennsylvania.  (AP Photo/Carolyn Kaster)

But many others on the left have also called on Breyer to step down, including MSNBC opinion columnist Mehdi Hasan. He had some harsh words for the justice in a column on Thursday.

"It's hard to pick which words in that statement I find the most naive, misguided and self-serving," Hasan wrote of Breyer's speech. "[W]here on Earth has he been over the past two decades as the Supreme Court delivered one partisan decision after another? Napping?"

Hasan was specifically responding to a statement Breyer made saying that it's important for the public to see judges as nonpartisan. Breyer further said he believes his fellow justices take their oath to be unbiased seriously.

"If the public sees judges as politicians in robes, its confidence in the courts and in the rule of law can only diminish, diminishing the court's power, including its power to act as a check on other branches," he said. "My experience of more than 30 years... as a judge has shown me that once men and women take the judicial oath they take that oath to heart. They are loyal to the rule of law, not to the political party that helped to secure their appointment."

BIDEN ORDERS STUDY ON 'SIZE' OF SUPREME COURT, OTHER POSSIBLE CHANGES AMID LIBERAL COURT-PACKING PUSH

Sen. Sheldon Whitehouse, D-R.I., also slammed Breyer for his speech. 

"The problem, Justice Breyer, is not those who refer to justices by the president or party that appointed them, it is the trail of 80 5-4 partisan decisions by Republican Justices giving victories to big Republican donor interests," he said. 

But Breyer made multiple other points arguing that the Supreme Court had indeed built up strong credibility, and that to make structural changes like court packing to get desired political outcomes would only harm that. 

"Our power, the court's power, has to depend on the public's willingness to respect its decision," Breyer said. "Respect even those decisions they disagree with... even when they think the decision is seriously mistaken."

He specifically cited Bush v. Gore in 2000 as a case where that was apparent. 

"Harry Reid, the Senate leader, a Democrat who probably also thought that that decision was wrong, later said that the most remarkable feature of the decision could have been ... the nation followed the decision without violent riots, without the throwing of stones in the streets. And the losing candidate, Al Gore, told his supporters, 'don't trash the Supreme Court,'" Breyer said. 

Supreme Court Associate Justice Stephen Breyer during a group portrait session in Washington, D.C., on Nov. 30, 2018. (REUTERS/Jim Young)

Supreme Court Associate Justice Stephen Breyer during a group portrait session in Washington, D.C., on Nov. 30, 2018. (REUTERS/Jim Young)

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The justice also noted cases upholding the Affordable Care Act, the right to abortion and the fact that the Supreme Court did not step in to help former President Trump in his election challenges as evidence that even justices seen as conservative are dedicated to the rule of law. 

"These considerations convince me that it is wrong to think of the court as just another political institution and it is doubly wrong to think of its members as junior league politicians," Breyer said. 

"The rule of law has weathered many threats, but it remains sturdy. I hope and expect that the court will retain its authority. An authority that my stories have shown was hard-won," Breyer added as he wrapped his remarks. 

"That authority, like the rule of law, depends on trust... that the court is guided by legal principle, not politics," he continued. "Structural alteration motivated by the perception of political influence can only feed that latter perception, further eroding that trust. There is no shortcut."

Fox News' Marisa Schultz and Evie Fordham contributed to this report.