For all those already making grand strategy for 2020, consider!
Suppose, for the sake of argument, that after three years, Trump decides he's done enough bomb-throwing, and it's time to spend more time with his family instead of running for a second term.
After the primary is done, the Democrats, having worked up a full head of steam preparing a massive anti-Trump campaign, might find themselves actually confronting Tim Scott.
There are times that taking generic "stop the Republican" bumper sticker slogans and filling in the name at the last minute just doesn't work, and that would be one of them.
(Ted Cruz would not be a good follower for Trump. In terms of restoring the mangled structure of the legal system, yes; in political terms, no. We'll need someone well-spoken and unifying. The Republicans have a few options already visible; the Democrats don't.)
Afterthought: Suppose, further, that Trump plays the Democrats' game and rigs the primary. Doesn't have to involve actual dirty tricks; he could just hold off on a public announcement of his planned retirement until opening day of primary season, while coordinating for several months ahead of time with his chosen successor.