The biggest problem the Germans had in stopping the Nazi gains in the election of 1933 that resulted in Hitler as chancellor was that a substantial faction of the vote, the Communists, refused to cooperate with the centrists in order to block him. It kind of reminds me of something more modern but I can't seem to put my finger on it.
I don't think the progressives, like third party candidates are an issue this time around. Hitler and the Nazi's gained some power (33%) and used it as the thin edge of the wedge, burning down the parliament was an excuse for an emergency decree and Goering (Barr) was in charge of the cops, game over.
America has stronger democratic institutions, traditions and a deeply instilled democratic culture, but a white racist majority who are teetering on the brink of tribalism, Trump still has a majority of the white vote, it's almost the only support he has. He still has some Blacks, Hispanics, Asians and Jews who support him, in spite of what he has said and done, 33% of every culture on earth are complete arseholes, but not all of them are suicidal, hence Trump has less than 5% black support.
I believe it will be to big to rig Baldrick, but Trump will still try, both because he is desperate and knows prison awaits (so does Barr) and because he is fucked in the head and cannot admit defeat. He will whine about a rigged election until he is muzzled and jailed by a judge, soon after the election.