It is interesting to see how you have the spark of mind to include this option back in december 2019.
The BLM / Floyd situation (not yet resolved) is a little bit early in the year to have an impact on the November elections (ie cancel them).
But who knows.... maybe more riots for later in the years (BLM or other social issues) and the martial law might be invoked.
As you can see by the reference to Martians I wasn't particularly serious about that possibility back then but with Trump's authoritarian leanings I think there's a non-zero chance of him trying to push the election around if he sees it not going his way. Rioting provides a good excuse it's just that it might not last until November. However... given the year we're having there could well be some other crisis or two at the convenient time. Even friggin' Martians are probably looking at this shit and thinking "let's just put face masks on and invade, nobody will see it coming".
Sadly I don't think anyone on Earth right not would be surprised if we had a real UFO sighting and aliens started invading. Shit would probably be thrown into the 'WHAT THE FUCK IS 2020 pile'
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.
Still a long long way to the election folks. Comey changed the fate of the Clinton vs Trump election 6 (I think) days before the race by announcing that the case against Clinton was reopening.