If Pete Buttigieg wins the nomination: His inexperience and embrace of many extreme positions (which he doesn’t seem to realize are, from the viewpoints of a great many Americans, truly extreme, especially his abortion absolutism), means Trump wins.
If Bernie Sanders wins the nomination: The exposure of his years lionizing communist dictatorships, which his fellow Democrats have given him a pass on (hoping to pick up his supporters), and the far-left economic-redistributionist policies he still holds mean Trump wins in a landslide.
If Joe Biden wins the nomination: He increasingly seems old and befuddled and Trump wins.
If Mike Bloomberg wins the nomination: Trump is the “blue-collar billionaire”; Bloomberg is just a globalist capitalist who champions policies that hollowed out industrial America. Trump wins.
If Elizabeth Warren wins the nomination: She won’t.
If Amy Klobuchar wins the nomination: At this point, she’s a wild card who, if she hews toward moderate, centrist positions, has a shot. But she hasn’t really been tested and vetted, so odds are still Trump wins.