Absolutely not. You are not allowed to fire someone based on their political beliefs, especially in California. You are forced to accept people in society regardless of your personal beliefs.

Also, plenty of people is a vague term, they are less than 50% of the democratic party to put Clinton and Sanders as their representatives. The soldier who also ran was what was left of the old "liberal" party. He echoed the sentiments of 1990's Bill Clinton and he was left behind with nary a backer.