I think there is enough evidence of attempts to rig every single US election in my lifetime (between gerrymandering, voting machine malfunctions (hanging chads), unconstitutional election law changes in some states, organized smear campaigns, burying harmful news stories, etc.) that it's reasonable to say that any of those elections was rigged. I also think that there's no evidence that any of those rigging attempts changed the outcome, so it's reasonable to say that any of those elections were not rigged.

As far as I can tell, the only unreasonable position is that US elections are always completely and perfectly clean. People commit fraud to win county clerk elections - every more significant position almost certainly has some dirty games.