Elections are NOT going to be cancelled. I highly doubt that Trump is going to be able to pull off some fucking Frank Underwood shit from House of Cards to try to sway this his way.
Doesn't need to be cancelled... postponed until we got law&order reestablished, or until we got a vaccine, or until that Martian situation is dealt with.
There are other options too. E.g. impose strategic curfews/quarantines/anti-Martian blockades in places that (completely coincidentally) tend to vote for Democrats. Or just
ask China for help LOL.
if he postpones it without setting a new date right away i would be very worried.