No, that’s not going to happen. There’s no mechanism to make that happen.
Why would they have to cancel the election when they can just manufacture the results they want?
Yes, there is. After the violence at the 1968 Democratic Convention in Chicago, Lyndon Johnson feared that the antiwar youth and the Black Panthers would join forces and mar the election campaign with terrorism. He asked the NSC to war-game scenarios in which the 1968 election could be postponed.
The NSC lawyers came back with an option that would have LBJ annul the Constitution, declare martial law, call out the military, and then, once order was restored, set new dates for the elections and restore the Constitution. Johnson signed off on this. Fortunately, the Black Panthers saw the antiwar youth as useless dilettantes, and nothing came of it.
This all became public after Nixon's resignation when the Post and the Times wrote a series of articles on the "White House horrors."