The Democrats work very hard to keep other political parties’ candidates off the ballot (see: Green Party in Wisconsin this year for example). They don’t go aft

The Democrats work very hard to keep other political parties’ candidates off the ballot (see: Green Party in Wisconsin this year for example). They don’t go after republicans (as a party) for the same reasons republicans don’t go after them. The other party has enough resources to defend themselves, and they need each other to play the foil in elections so as to maintain the facade that Americans are making a real choice. Republicans work about as hard keeping more right-associated candidates off the ballot (e.g. libertarians).