Two potentially blockbuster Supreme Court decisions on abortion access and guns are fueling calls from the left to add seats to the nation’s most powerful court — increasing the pressure on President Biden and Democratic lawmakers who so far have resisted such far-reaching changes.

The White House’s answer to the long-simmering liberal anxieties over the judiciary has been largely academic, putting together a commission of three dozen legal experts tasked with examining potential structural overhaul of the courts. That panel meets for the first time in public on Wednesday afternoon.

But activists say the Supreme Court’s announcement Monday that it will review Mississippi’s ban on nearly all abortions after 15 weeks of pregnancy — a case that supporters and opponents alike say could erode the landmark Roe v. Wade — underscores their concern that Biden’s current tack on the judiciary is inadequate to confront a conservative court majority that could overturn the decades-old precedent legalizing access to the procedure.

Democratic presidential nominee Joe Biden initially dodged questions in October 2020 about whether he would pack the court before saying he opposed it. (JM Rieger/The Washington Post)

“The more the court forces the issue, the more that Democrats will understand that they can’t wait,” said Christopher Kang, chief counsel of Demand Justice, a liberal advocacy group that focuses on the courts. “They can’t wait in particular for a commission that is not even going to make recommendations. I think all of the facts that the Democrats need to know are already out there.”

The debate within the Democratic Party over the courts encapsulates the tensions between an impatient activist base and Biden, a classic institutionalist who has been comparably slow to embrace structural changes that would upend how the legislative and judicial branches operate.

On the campaign trail, Biden largely resisted the push from the left to overhaul the judiciary, saying he was “not a fan” of adding seats to the Supreme Court. His view had some extra gravitas, considering his history as a former chairman of the Senate Judiciary Committee.

Justice Stephen G. Breyer — who is being pressured by some activist groups to vacate his seat this year to ensure an appointment by Biden — also has warned about the potential consequences of expanding the Supreme Court, arguing that it could dilute public confidence in what is supposed to be an apolitical branch.

But that has done little to satisfy liberals who are still reeling from the judicial battles of the Trump presidency, which successfully installed three justices to the Supreme Court and more than 200 conservative jurists — many young and able to serve for decades — throughout the federal bench.

“Congressional Democrats cannot wait and hope that the supermajority of conservatives on the bench do the right thing in this case or any of the other critical cases pending in front of them. They will not,” said Meagan Hatcher-Mays, the director of democracy policy for the liberal activist group Indivisible. “So Democrats must act. They must expand the court before millions of women and those who need reproductive health-care services become collateral damage.”

As aggressive as some on the left have been in embracing court expansion, many members of the Democratic caucus on Capitol Hill have, like Biden, been reluctant to endorse dramatic structural changes. The fact that the fate of the Roe decision could be at risk as early as next year has done little to alter that dynamic, even among supporters of access to abortion.

“I’m not convinced that that’s the right answer,” Sen. Tim Kaine (D-Va.) said of expanding the Supreme Court. Instead, he said, Biden’s court commission was the “right approach.”

Noting that he is a former federal appellate clerk and litigator, Kaine added: “I don’t think you tackle an issue this momentous — especially Congress tinkering with the Article III branch — without carefully looking at it.”

Sen. Jeanne Shaheen (D-N.H.), who said she was “disappointed but not surprised” at the Supreme Court’s decision to take up the Mississippi abortion case, said the news nonetheless did not change her views on adding seats to the Supreme Court.

Opponents of abortion rights, hopeful about the justices’ announcement this week to take up the Mississippi case, dismissed the renewed push to expand the Supreme Court.

“Quite frankly, it’s silly,” said Carol Tobias, the president of the National Right to Life. “Courts have gone back and forth in philosophy, depending on who has appointed various judges. Right now, because President Trump appointed three justices, the abortion movement, the abortion industry, is concerned that it’s going to impact the policies, but that’s the way it’s been working for a couple hundred years.”

Biden’s commission, unveiled last month, is composed of 36 legal academics, attorneys and former judges and is co-chaired by Bob Bauer, who was a top lawyer on Biden’s presidential campaign, and Yale Law School professor Cristina Rodríguez.

The left has been irritated at the inclusion of conservatives such as Harvard Law School professor Jack Goldsmith, who served in the Justice Department under President George W. Bush. The commission also features a panoply of liberals including Laurence Tribe, a professor emeritus at Harvard Law School, and Sherrilyn Ifill, president of the NAACP Legal Defense Fund.

The commission’s first meeting, on Wednesday, is expected to be largely administrative, but the group is tasked with producing a report on the issue by fall.

As that commission kicks off its work, most liberal activists have lined up behind a bill written by Sen. Edward J. Markey (D-Mass.) and Reps. Jerrold Nadler (D-N.Y.), Hank Johnson (D-Ga.) and Mondaire Jones (D-N.Y.) that would bulk up the number of Supreme Court justices from nine to 13, one justice for each court in the 13-court federal appellate circuit.

Nadler chairs the House Judiciary Committee, so activists considered his sponsorship a major coup, considering that he leads the committee that would oversee policies to revamp the courts. But House Speaker Nancy Pelosi (D-Calif.) does not support the measure and has deferred to Biden’s commission instead, leaving unclear how far that legislation will advance in either chamber of Congress.

“It certainly increases my concern that they’re going to overturn Roe v. Wade,” Nadler said. “That I think further shows the need” for this bill.

Proponents of expanding the Supreme Court — which critics deride as “court-packing” — also point to another move by the court to hear a major case, this one on guns, as reason to move expeditiously to add justices. That challenge, backed by the National Rifle Association, involves a New York state law that requires anyone who seeks a permit to carry a concealed weapon to show a special need for such self-defense.

But the Supreme Court’s decision to take up the Mississippi abortion case next term presents perhaps the most acute risk to Democratic priorities.

Eleven states have “trigger bans” in place that would outlaw abortion immediately if Roe is struck down, according to abortion rights groups. Liberal advocates are rallying support for federal legislation that would effectively codify abortion access into law, rather than relying on the Supreme Court to uphold decades of precedent.

Maintaining access to abortion is generally popular, according to public polling. In April, the Pew Research Center found that 59 percent of those surveyed said abortion should be legal in all or most cases, compared with 39 percent who said it should be illegal in all or most cases.

“We think that all options should be on the table when we’re talking about restoring our democracy,” said Christian LoBue, chief campaigns and advocacy officer at NARAL Pro-Choice America, of a potential Supreme Court expansion. “We recognize that this has been an ongoing effort over the last four years and beyond to stack the courts with anti-choice ideologues.”

Other prominent abortion rights groups, including Planned Parenthood, said they back efforts to add judges to lower-level federal courts and have kept an open mind on other proposals.

“We’re clear that the court has to be a priority for the Biden administration,” said Alexis McGill Johnson, president and chief executive of Planned Parenthood Action Fund. “We are encouraged they’ve formed a commission that is committed to examine what might be necessary.”

On the Mississippi case, Johnson warned: “This is absolutely a direct challenge to Roe.”

Emily Guskin contributed to this report.