*$300M on Betfair alone by late October
So the real figure is probably on the order of billions of dollars.
The media may very well not give Trump as much attention as back in 2016, without that many will probably forget him unless Biden turns out to be less likeable than Trump. Not to mention his advancing age which could be another hindrance.
It is weird to see this many Trump fans in bitcointalk as well but considering dude got 70+ million votes from just USA and probably have some fans overseas as well, I would say there are at least 100+ million Trump fans in the world and obviously having some here is not shocking.
Much more than that, actually:
https://www.pewresearch.org/global/2020/01/08/trump-ratings-remain-low-around-globe-while-views-of-u-s-stay-mostly-favorable/Many of them are ignorant of his actual policies, or are his fans due to cultural factors (e.g. the populist right in Europe), or due to a single issue (e.g. some Asians due to Trump's foreign policy and his attitude towards China).
The only way as it can influence on gambling industry is if Trump will win trough court and many books will be in hard situation, because some of them already accepted results with Biden and already awarded people which bet on Biden.
At least legacy gambling places accept fiat and know the identity of the bettor, it would be interesting if any of them would want to (try to) go after their customers and clawback the money they already paid out. Probably not, but at least BTC and altcoin gamblers don't even have to entertain such thoughts.