Your argument makes great sense if you ignore the actual American electorate. In the last election, virtually all of the Democratic Party gains in the House were due to victories by moderate and conservative members of the party. The more radical wing gained by taking over safe Democratic seats in the primaries. The Resistance Democrats will be able to force a prospective nominee far left. They will make the nominee kowtow to identity politics and political correctness. The nominee will have to embrace every pie-in-the-sky plan. They will insist on gun confiscation and abortion on demand until birth. They will demand open borders and sanctuary cities. The more extreme these positions become, the more room they will leave in the middle. In that scenario, a Bill Clinton type of centrist could do so well in the South and Midwest that the Democratic Party candidate would finish a distant third in ten states.