Elections will be mostly fair in most of the blue states and in a few safe red states. But as we can see from the redistricting fiasco, elections can be rigged far ahead of the actual voting.
But in the end, if an actual blue wave took place with the effect of flipping either or both houses, I would think there’s a distressingly high probability that Trump and his minions would cause so much chaos around the results that the newly elected Democrats won’t be allowed to take their seats the following January 3.