They absolutely, 1000% need Democrats to win. Maybe not their respective districts, but if they want to get anything done on a national level, they need about half the country on their side, and that includes Democrats.
Now, they can certainly eat the party whole, the way the tea party and MAGA ate the GOP. That involves being more specific than "Democrats bad". In fact, how did they do it? Did you ever see them telling people to abandon the Republican party?
It's always easier to completely rewrite code from scratch than to make small modifications to an existing project.