I'm pretty much panicking over another Trump presidency, but simply selling every stock you own is almost certainly a bad idea.

First, there's a pretty good chance that whatever else goes wrong the Republicans absolutely care about keeping stock prices up.

Second, even if the market does crash, having an index fund is at least a good way to insure that you more or less keep up with everyone else. E.g. it prevents a scenario where you get dropped into a worse economic situation and then left there when things eventually improve.