There's plenty of bookies offering much better odds than that.If you stand to win more than 800, I probably would take that bet. I can't imagine you got much better than a 1:5 from a bookie.
Fractional format, but presumably you can follow those - bet365 have Biden at 1/2. Paddy Power have him at 2/5. Betfred have him at 8/15. Other places have similar kinds of odds - some of them are at 4/9 or 4/11. Pretty much anywhere that someone places a US$4000 bet, they'd be getting better than a US$800 profit.