The Democrats wanted the USPS to deliver the mail. They also wanted people to be able to vote through the mail because we are in the middle of the worst pandemic in 100 years. This is different from treating the USPS as a general voting system.

You are arguing that the Democrats cheated more than the Republicans, or "better". Do you have any evidence of this? This needs to be evidence from the past election, not Chicago in 1962 or something.