For a Supreme Court that seeks to defend the legitimacy of its rulings as rooted in the law and not political ideology, what unfolds over the next few months is poised to be a historic test of its reputation.

The Senate will hold a contentious confirmation vote to fill the seat of the late Justice Ruth Bader Ginsburg with a reliably conservative President Donald Trump appointee.

The appointee, who Trump says will be a woman announced this week, would deepen the court’s conservative tilt potentially with immediate consequences for divisive areas such as abortion, gun control and more.

A case set for argument Nov. 10, just days after the election, threatens the whole 2010 health care law known as Obamacare, which the court has upheld in previous challenges.

And the justices could be called on to decide the heated presidential election, where Trump already has challenged the integrity of the outcome if he loses to Democratic nominee Joe Biden.

How the justices act in those situations — and how much the public retains confidence in them throughout — could wind up galvanizing calls from some Democratic lawmakers and their allies to change Senate rules to remake the high court in the coming years.

The Supreme Court plays a key role in the government because it makes many difficult decisions the political branches are unable to make, said Paul Smith of the Campaign Legal Center, a veteran litigator before the court.

The public accepts those Supreme Court decisions “because they view the court as something other than a purely political institution,” Smith said. “At the court, if it loses that completely, it will cease to function in the way it needs to.”

A move by Senate Republicans to confirm a third Trump appointee to the court in a presidential election year, when four years earlier they blocked President Barack Obama’s nominee ahead of the election, already drew calls for changes to the structure of the court such as additional justices or eliminating their lifetime tenure.

Republicans ultimately confirmed Trump appointee Neil M. Gorsuch to fill that vacancy in 2017, which led some Democratic lawmakers to refer to it as a stolen seat.

Brian Fallon, the executive director of liberal advocacy group Demand Justice, tweeted any Trump appointee confirmed “at this point in the calendar would be fundamentally illegitimate, and Democrats must be prepared to act accordingly.”

If that third confirmation happens, Massachusetts Democratic Sen. Ed Markey tweeted, “when Democrats control the Senate in the next Congress, we must abolish the filibuster and expand the Supreme Court.”

Senate Democrats would need at least four Republicans to vote against Trump’s third appointee to thwart the confirmation. Short of that, Trump’s pick would likely add a solidly conservative vote on policy issues such as abortion, gun control laws, immigration, LGBT rights and voting rights.

Last term, Chief Justice John G. Roberts Jr. established himself as the center of the court, but that now could be in jeopardy. He has talked about his overriding concern to use his perch as chief justice to maintain the legitimacy of the court as nonpartisan — and his actions last term navigated the Supreme Court into calmer waters.

Roberts joined the four justices on the liberal wing in surprising ways, to strike down a Louisiana law that would restrict abortion access and turn aside Trump’s effort to rescind an Obama-era immigration policy that allowed those who arrived in the country illegally as children to work and avoid deportation.

With a third Trump appointee, “it may very well be Chief Justice Roberts is not in a position anymore to make those votes that go against the grain and show the respect for law in an effort to make the court seem political,” Smith said. “He won’t be the fifth vote anymore.”

That also would loosen Roberts’ grip on which cases the court agrees to decide, and how sweeping those rulings can be if they strike down laws or reverse Supreme Court precedents such as the 1973 landmark decision in Roe v. Wade that established a constitutional right to abortion.

Sen. Josh Hawley, a Republican from Missouri on the Judiciary Committee, was reacting to the court’s decisions last term when he said he would only vote this year for Supreme Court nominees “who understand and acknowledge that Roe was wrongly decided.”

He called on fellow Republican senators to take the same stand, a stance that could be seen as stripping away pretext about the ideological policy outcomes conservatives want from the justices they confirmed to the bench.

Stress test

The despair of Democrats and their allies would only deepen in the case about the 2010 health care law. Before Ginsburg’s death, legal experts expected Roberts and to join the liberal wing to provide enough votes to uphold the bulk of the law.

But with only eight justices, a 4-4 vote would essentially uphold a lower court ruling that struck down the entire law, including provisions that require coverage for those with pre-existing conditions.

The court has appeared conscious of its reputation before. In 2016, when the court was shorthanded after the death of Justice Antonin Scalia, the justices appeared to dodge contentious political cases that might evenly divide the court.

The ultimate status of the court after a third Trump appointee will depend on the elections of 2022 and 2024, said Bruce Ackerman, a law and political science professor at Yale University who has written about turning points in American constitutional history and advocated for structural changes to the Supreme Court.

“If the Republicans continue to win in 2022 and 2024, the minority of bitterly disappointed Democratic voters will reluctantly begin to recognize that their opponents have won a ‘popular mandate’ from most Americans in support of the New Court’s deeply conservative constitutional principles,” Ackerman wrote in an email response to questions.

“If Biden wins, and the Democratic Congress enacts strong legislation reinforcing Obamacare and gender equality, the fact that McConnell rammed through a last-minute appointment will become especially significant if the new Justice joins with other Trump appointees to provide the crucial votes invalidating the Democrats’ progressive legislation,” Ackerman wrote.

At that point, efforts to add justices to undo the damage of the past becomes a very real possibility, Ackerman said.

“However the court-packing struggle turns out on Capitol Hill, it is sure to do long-lasting damage to the legitimacy of the Court over the next generation,” Ackerman wrote.

Alicia Bannon of the Brennan Center for Justice at New York University’s law school, in an op-ed on the organization’s site, used the court’s reputation to advocate for waiting to fill Ginsburg’s seat until after the election.

“It’s not simply another stress test for our institutions — there’s a real risk it will break them,” Bannon wrote. “That is genuinely scary — not just for the Supreme Court, but for the basic functioning of our country and the rule of law.”