Here is one possible explanation explaining Biden's prediction that wasn't included in the OP.
From the article...
The presumptive Democratic nominee latched on to Mr. Trump's earlier resistance to grant
COVID-19 federal relief money to the postal service, labeling the move "un-American." On April 10, the
postmaster general requested help, saying the service was at a "
critical juncture" and faced a net operating loss of more than $22 billion over the next 18 months.
Not financially assisting the postal service, Biden alleged, would be one way the Trump administration could impact proposed expansion of vote-by-mail efforts for the general election.
"Imagine threatening not to fund the post office. Now what in God's name is that about? Other than trying to let the word out that he's going to do all he can to make it very hard for people to vote. That's the only way he thinks he can possibly win," Biden said.