Baris & Barnes went over this. The Democrats burned up a lot of their 4 for 4 (ie voted in the last 4 presidential elections) voters doing mail in ballots. The Republicans have a lot of theirs left for voting day. What the Republicans have been getting to the polls are a lot of 1 for 4 and 2 for 4 voters (ie less reliable voters) so far.
Translation: the Republicans have plenty of ammonia left for Election Day. The Democrats dont.
Thanks