The U.S. Constitution states that state legislatures will determine the method by which they conduct elections, and do so prior to the election.
If the state legislature made provisions for using the National Guard to secure the election, then this may be legitimate. If not, it would be unconstitutional.
I hope GOP lawyers will wake up and challenge this. I think they should begin legal proceedings prior to election day. Early voting has already commenced. Has the National Guard had any role?
The word to use is UNLAWFUL from a state court ruling on actions taken during the election. That particular word, when used in a quo warranto action in Fed court, and evidenced by a state court, sets the legal threshold for any officeholder, including US Senators and Congresspersons. to overcome. And there is no presumption of 'right' to occupy a seat which could not be occupied due to an UNLAWFUL election.
IANAL (I am not a lawyer), but it seems a no-brainer to me.