Trump will publicly "discover" that the Democrats are "running an illegal alien voter fraud ring" in districts that are up in the air. Trump will send ICE and the National Guard to vet polling stations (read: intimidate/black-bag minorities). The Dems will hem and haw about how this is illegal but in a way where they do not put physical resistance/security up to combat these measures. This will decimate turnout for the disenfranchised. Liberals will post about how they have to let you vote if you stay in line and you have to stay in line even if they black-bag you.
There will be a case that goes to the Supreme Court about this that will only be resolved after the counts are finalized and will either say, 6-3, that a) this is illegal but we can't redo the elections because of it, or b) this is legal, fuck you.
Additionally, the democrat supporters will insist that the solution to this is to vote harder, and when polling comes out that minorities voted in lower numbers than previous years (because of the aforementioned intimidation) the dems will then blame minorities for the current state of affairs and tell them they deserve to be sent to the camps because they didn't vote.