There is nothing in the Constitution mandating that the Supreme Court have nine members, and a simple act of Congress could increase that number to 11, or 15, or even more. That effectively creates a way for a political party in control of the House, Senate, and presidency to add a large number of ideologically sympathetic justices to the Court, all at once.
Reading this gave me a hilarious/terrifying mental image of an exponentially growing US Supreme Court.
Whenever one party controls both congress and the presidency, they can add new justices to the court. The political pendulum swings every 8 years or so, so every 8 years two new members would be added to steal back that party's majority of the Supreme Court.
2016: 9 members. 2024: 11 members. 2032: 13 members. 2040: 15 members. And so on.
But we also need to take into account the justices that have to be replaced because they retire or die. Typically 1-2 justices get replaced every 8 years, but as the court grows larger, this number will increase.
Let's say no more judges get appointed during Trump, so when the Democrats are next able to expand the court size in 2024 they need to add just two more justices to make the Supreme Court vote 6-5 in their favour. Then during the next 8 years two justices need to be replaced, one on each side, and when Republicans win back the presidency + Congress in 2032, they need to appoint 4 justices to tip the 4-7 court into 8-7 in their favour. Then during the next 8 years, three justices need replacement, two of them Democrats who are on average older at this point, making the Supreme Court 10-5 in Republicans' favour. So the first thing Democrats do in 2040 is to appoint 6 new justices.
2016: 9 members. 2024: 11 members. 2032: 15 members. 2040: 21 members. And so on.
The size of the Supreme Court grows exponentially, doubling every 24 years or so. It will pass a hundred before the turn of the century, then a thousand some time in the next century.