The phrase, “Nail in his coffin”, comes to mind.
Conservatives will NOT vote for these stolen-election deniers. They just won’t.
Conservative voters don’t win or lose elections. Independents do, and independents don’t want to hear about 2020 when they can barely feed their families.
DeSantis is being smart here. Trump can and probably will win the nomination, but pretty much every independent in this country has a fully-cemented position on Trump. DeSantis is still largely unknown by independents, so it does DeSantis no harm and some good to stay out of the 2020 debate.