We are in a winner takes all system,
It has limitations, Its very stable with 1, primary party, its possible to have 2 primary parties, its while not impossible, very very hard to have more primary parties.
Sure its possible particularly in a state for a new party to replace an existing one.. However most cases of this the new party becomes part of or replaces an existing parties leadership. However if you really want more parties we need something like instant runoff elections, Im very disappointed in how much push back on that has happened where its been attempted. (or a parliamentary system.. but i dont see that fitting into the US system)