Wow. A second person here who gradiated from elementary school.
If there’s a significant difference between the down-ticket votes and the presidential votes within the party, that means that they voted or somebody voted for only the presidential candidate.
Some states do not allow “undervotes,” meaning ballots where the voter has not made a choice for each office. These ballots are rejected by the machine and the voter can correct the ballot on the spot.
I don’t know if that was true in these states or about the effect of the theoretically mailed in last minute ballots.