The Supreme Court of Pennsylvania overrode the legislature of that state regarding election rules, which on its face looks like a violation of the US constitution. From Alexander Macris at macris.substack.com:
If you’ve been following the mainstream media, you’ve probably read that Trump intends to file a lawsuit in Pennsylvania to “stop counting votes.” Most likely, this has been presented as an outrageous evil, unjustifiable by any standards of common decency, and grossly unconstitutional. Is that really the case? Or is it more complex than that?
There will be a lawsuit, no doubt; and it will involve a lot of votes being thrown out. The plaintiff (Trump and/or the Republicans) will win, because Pennsylvania’s highest court has almost certainly violated the Constitution of the United States. That’s why, in the weeks ahead, the Supreme Court of the United States (SCOTUS) is going to rule in favor of Trump.
Let’s wind the clock back about a week to explain how we got here.