If I could wave a magic wand and undo a Presidency, it would be Reagan's.
Trump was a big loud stupid animal, but almost completely ineffective at legislative work. McConnell carried all the water of his few cruel "accomplishments." All Trump wanted to do was hear/see himself talk/tweet. He thankfully got in his own way a lot.
Reagan, on the other hand, was competent evil, and his malice towards American peasants is felt by most of us every day whether we realize and acknowledge it or not. One of the few people I can say without an ounce of guilt or shame deserved the traumatic way he died and far worse.