Democratic Primaries

Sadly, that's just a guess. Even if you listen to the most knowledgeable experts, you're still guessing. Even if this is a correct guess, it doesn't follow that the number of new cases will fall as rapidly as they increased. I believe the more likely scenario is that the number of new cases will hit a plateau and remain roughly constant until the virus has run its course through the population and/or a vaccine becomes available.

The idea of social distancing is to slow down the spread of the virus so that our healthcare system doesn't get overwhelmed. It isn't expected to significantly reduce the number of cases, just spread them out over a longer period of time. Postponing the election will likely mean voting at a time when the daily number of new cases is higher than today, not lower. I believe that the number of asymptomatic carriers of the virus and the risk of infection will be higher in June, not lower.

It's also a dangerous precedent that creates an extraordinary opportunity for abuse.