Markets prefer political stability. Average annual S&P 500 returns are around ~7% adjusted for inflation, but ~12% when a President is in his second term.
Political answer:
A Trump loss would be presumably be to one of the self-avowed socialists running which would certainly crash the markets.
Furthermore, even without a market crash, a socialist implementing mark-to-market capital gains taxation while also doubling the long-term capital gains rates (15% to 32% for me) would drastically slow down my march towards $1,000,000.