The Left tries to control us by creating a drumbeat. They get the news and all their faces from Congress, prior office holders etc repeating the same lies and half truths to create a gestalt that there is no honest disagreement. They embolden each other.
When POTUS makes a tweet like this instead of pushing back he is agreeing, woah, this is so bad we better put off the election. It cuts the legs out from under them because suddenly the whole chorus they created is reinforcing POTUS point that this is serious enough to delay the election.
That puts them in disarray and the chorus needs to work up a more nuanced message.
POTUS uses that time to push back on the fake facts.
Nobody is talking about postponing the election except Trump. Nobody is going to talk about postponing the election except Trump. Nobody wants to postpone the election except Trump. It would need congressional approval and no House member is going to vote for a bill that would put them all out of office. No Senate member would vote for a bill that would put a third of them out of office. If this is some kind of troll then it's a waste of time.