Ya, you have to look at what he is responding to... The left keeps claiming there is "no evidence" that mass mail in voting leads to fraud or other problems - meanwhile in NY they did a mass mail in voting election, 25% of the ballots were throw out and they still don't know who won 6 weeks later. They are probably going to have to hold another election. Very similar story happened in New Jersey. It's happening right now, these horrible outcomes, and the left still claims there is no evidence of it, and they are pushing for mass mail in voting. They are acting dishonest and insane.
Trump floated the idea so that the left realizes that they need to behave and hold the election in a fair reasonable manner. If they think masks work, then wear them to the polls. Ask for an absentee ballot, that's always a good option.
Trump will not delay the election if they behave and hold a regular, at least fairly fair election. He just wanted to put all his options on the table so he has some leverage so hopefully they won't keep acting up.