Expanding the Supreme Court to more than nine seats sounds like a radical idea, and the term for it, “court packing,” sounds derisive because it has created controversy every time it has come up. But it has been attempted — and done — in American history before.

Now the idea is back in the political discourse as some Democrats, frustrated that the Supreme Court could get even more conservative in the coming months, push presidential nominee Joe Biden to consider it if he wins the White House and Democrats take back the Senate majority. Republicans paint that as sour grapes.

Biden doesn’t want to talk about it — both he and vice presidential nominee Kamala D. Harris avoided direct questions in their debates about whether they’d support packing the courts. “Whatever the position I take on that, that will become the issue,” Biden replied to moderator Chris Wallace in the September debate, an answer that acknowledges what a sticky political issue this is.

But there is a world in which Biden may warm to it and attempt to push through legislation. Here’s what court packing is, its history and how it could happen.

What is court packing?

Court packing is adding more judges to a court than there are now, something that can be done on the federal level simply by passing a law.

The Constitution says nothing about how many justices there must be on the Supreme Court, and over time, the number has fluctuated. The court started out with six justices, expanded to seven and has gone as high as 10. Congress set the Supreme Court to be nine justices in 1869, but if a president and Congress agree, they could change the law to expand the court or shrink it.

What’s the argument for adding justices to the court?

Doing so would change the political makeup of the court and influence its decisions. Congress and the president might decide that the court majority is too far out of line with their understanding of the Constitution and the law or public opinion, and then add seats and fill the court with justices who think more like them in the hope of rebalancing the scales.

“Since justices effectively can’t be fired, except by impeachment, the idea of court packing is to dilute their vote,” Georgetown University law professor Josh Chafetz said in an email to The Fix.

A brief history of court packing

In the Civil War era, the court expanded and shrank like an accordion. In 1863, the Republican Congress expanded the court to 10 justices to give President Abraham Lincoln an extra appointment. A few years after, Congress reduced the court to seven justices to prevent President Andrew Johnson from making any appointments, and then expanded it to nine in 1869 to give President Ulysses S. Grant vacancies. It has stayed at nine ever since.

But other presidents have tried to change it. President Franklin Delano Roosevelt tried in the 1930s to get Congress to expand the court, frustrated by how it was knocking down pieces of his popular New Deal legislation. He put out a judicial overhaul plan that would allow him to appoint a new judge in all federal courts for every judge older than 70. “That’s the way it was dressed up, but people saw pretty clearly what it allowed him to do,” said Russell Wheeler, a Supreme Court expert with the Brookings Institution, “which was to aim to appoint justices for the five or six who were over the age of 70 on the Supreme Court.”

Roosevelt’s idea hit a wall in Congress. But in a roundabout way, he got what he wanted: The court saw its majority imperiled, and two justices began switching their votes to support New Deal legislation. “It’s called ‘the switch in time that saved nine,’ ” Wheeler said. “They switched their approach to New Deal legislation, and that saved the idea of nine justices.”

Why some Democrats are talking about packing the court now

They’re frustrated about how the newest two justices, Neil M. Gorsuch and Brett M. Kavanaugh, have gotten on the court: under extremely politically divisive circumstances, nominated by a president who lost the popular vote, and approved by a bare majority of a Senate that, because of where people live, no longer represents a majority of the population.

“Any one of these things might not have been sufficient by themselves,” said University of Michigan assistant professor of law Leah Litman. “But the combination of all these things … strikes people as no way to run a country.”

“Nothing is off the table,” Senate Minority Leader Charles E. Schumer (N.Y.) told fellow Democrats in a widely reported private conference call this weekend. He didn’t specifically mention court packing, but this was interpreted as a nod to considering the idea, since he didn’t rule it out.

Expanding the court gained traction during this year’s Democratic presidential primary. As many as 11 candidates were at least open to it, according to a Washington Post tally. “It’s not just about expansion, it’s about depoliticizing the Supreme Court,” Sen. Elizabeth Warren (D-Mass.) said. “It’s a conversation that’s worth having.”

“We need to reform the Supreme Court in a way that will strengthen its independence and restore the American people’s trust in it as a check to the presidency and the Congress,” former South Bend, Ind., mayor Pete Buttigieg said.

What Biden has said about court packing

He has not been a fan. He sees it as a maneuver that could come back to haunt Democrats when they’re out of power. What’s to stop a Republican president and Republican Congress from expanding it even more, to get what they want? That was a feature of the Reconstruction era. “We’ll live to rue that day,” he said last year during the primary.

Plus, Biden has served in the Senate for more than 30 years and has a reputation for respecting institutions and the way things are done. He’s an unlikely candidate to be the first president in some 150 years to expand the court. And his campaign seems aware of a risk that even talking about this could turn away moderate voters — who may not be as conservative as the way this Supreme Court is heading but who also don’t want to mess with the way things are done. Ginsburg was opposed to it for that reason.

“If anything would make the court look partisan,” she told NPR in 2019, “it would be that — one side saying, ‘When we’re in power, we’re going to enlarge the number of judges, so we would have more people who would vote the way we want them to.’ ”

My Post colleagues report that some people in Biden’s campaign are annoyed by this movement rising on the left. “People in your own party shouldn’t cause you problems 44 days out,” said one Biden adviser, criticizing Democrats in Congress for elevating the idea.

How this could still actually happen

Let’s say Democrats are in a position to seriously consider this: They win the presidency, keep control of the House of Representatives and win the majority in the Senate, thus controlling the White House and all of Congress.

Considering there is a pandemic and calls for action on racial injustice, moving to expand the Supreme Court doesn’t seem like the first to-do item on their list. But what if Democrats start passing Biden’s agenda, and inevitable challenges by Republicans make their way to a conservative Supreme Court, which stops some of the legislation?

There could be a world in which Biden, frustrated by the court just as Roosevelt was, starts thinking differently about the court’s makeup. Biden would need majority votes in the House of Representatives and in the Senate to approve expanding the court, just like any other piece of legislation (though Senate Republicans could try to filibuster it). If the law passed, he and the Democratic Senate could add justices with a simple majority vote.

There’s also a world in which even just talking about changing the court actually changes how partisan the court is, like what happened under Roosevelt. Packing the court has ramifications for the justices as much as the politicians who do it.

“It will be a severe blow to the legitimacy of the Supreme Court if people look at it say: ‘This is a compromised court, with these judges appointed by a minority president,’ ” Wheeler said.