Last I checked Senators were elected by state voters and not by national voters.
Can you name a POTUS election year that voters reelected a POTUS, but voted out those in the same party?
Is this what you base your 'guess' on?
Don't you have any state data to backup your 'guess'?
State voters elect POTUS and Senators the same day, often with a straight party vote.
RATS seldom split their ticket in POTUS election years.