SCOTUS is unchecked by the rest of the federal government. The only thing that would limit their power is a constitutional amendment, which requires 38 states to individually ratify it at the level of their state governments, not their federal congresspeople.
There is literally no way for congress to affect the supreme court once it has 9 justices, or contradict its rulings on laws they call “unconstitutional”, short of impeaching supreme court justices or packing the court with more than 9 justices. Once enough of the court is full of fascists or enablers, it’s EXTREMELY hard to escape fascism without a constitutional convention.