Four years ago, then-President Donald Trump rallied his supporters to march to the U.S. Capitol and urged his vice president to stop the congressional certification of Democrat Joe Biden's victory.

Democratic and Republican lawyers already have gone to court over these issues in the run-up to Tuesday's election. A Pennsylvania case at the Supreme Court pits Donald Verrilli, who was President Barack Obama's top Supreme Court lawyer, against John Gore, a onetime high-ranking Trump Justice Department official. Mailed ballots that don’t come inside a secrecy envelope have to be discarded, under a state Supreme Court ruling. The Supreme Court left that order in place in response to a Republican effort to block it. “This is a horrible thing that the United States Supreme Court has done to our country," Trump said in Pennsylvania Saturday.