I believe Moscow Mitch is trying to prevent or slowdown a new stimulus bill for one reason: He knows that bill will include funds to implement national vote by mail and enhance election security. He is terrified that national vote by mail will upend GOP voter suppression efforts, especially those designed to make physical voting more difficult.
The longer it takes to pass such a bill, the worse the chances that we will be able to have a proper vote in November, hence the delay.