There will be suits in state courts.
There will be appeals to the legislatures to select the electors.
There will be appeals to federal courts.
There will be cases argued before the Supreme Court.
The final option belongs to POTUS alone—use of the military to round up the traitors and impose martial law as enemies, foreign and domestic are rooted out. This is his obligation under his oath of office.
He can even call out armed Americans to assist.
This is all legal and Constitutional.
President Trump is not going to allow America to be stolen.