Like all fascist thugs in history have done, Biden was trying to scare and intimidate those who are planning to vote republican in this coming election into not doing so. He basically labeled anybody who won't be voting D and rightly so, as enemies of the state that will be facing retribution somehow. In Saul Alinsky fashion, he used Nazi turnspeak, accusing the other side of things you are most guilty of, such as "a threat to democracy..." when it's you and your party that have exhibited it the most.
Two years into a failed catastrophic presidency, and having nothing to show for, with disastrous poll and approval numbers looming, all they have left is a desperate attempt (which completely backfired) to change the discussion to the previous president as a last ditch attempt to resuscitate a party and presidency on it's deathbed.