Do these prediction markets pay interest? If not I'd rather not pay $0.915 for a $1.00 payout in three years.
This is a good question. It looks like Kalshi (which hosts the underlying market in question here) in fact does pay interest on both cash balances and open positions, at a reasonable market rate: 4.05%. https://kalshi.com/blog/article/interest-cash-open-positions
To add on this, prediction markets currently put Trump Sr. as 8.5% likely to win the 2028 GOP nomination (electionbettingodds.com). So, I wouldn't take your "he'll be done in four years" as certainty. The market thinks things are far more precarious than you do.