Hmm... Not so sure. Not like this at least.

I think you focus on Trump's chances of winning or one of his opponent winning. You forget all the cases where Trump simply can't make it to the election!
-he can be killed by any terrorist or violent activist (not like the guy is trying to appease people angry against him)
-he can simply die from natural causes or accident, the guy is 73 old it's not that unlikely
-he can lose his son or wife and be unable to continue the campaign for personnal reasons
-he can be... persuated to withdraw
-he can refuse to run being tired of doing this forst term, not like the job is easy or he needs the money/power

And I probably forget lots of them...
Betting on Bernie is completely underdog. Betting on "anything but Trump" has rather good odds in my opinion.

Such good odds that I would take up to 2BTC bet on this (with escrow if that's too high ofc)