There are a few differences. 1) No Republican supports them. 2) The far-right extremists seem to know more about biology and have more respect for the unborn. 3) The Communists/aka Democratic Socialists are much wealthier and better funded. and are supported by many well-known Democrats like Bernie, the Squad, Ro Khanna, and Kamala Harris.
Both groups decry capitalism, oligarchs, police, ICE and the current war with Iran because it doesn't benefit their goals for chaos and their lies.
Both groups hate Jews, Israel, and Trump. Tread softly if you are a Democrat. You are losing your party, your values and your minds.
If you can obtain a history book published before 1980, you'll see that USSR and Nazi Germany were cooperating (also included Islamists) to take over the world, then they began attacking each other. The USSR/Communists were far more lethal and killed millions more than the Nazis. Particularly Christians. They are now coming in the back door to achieve what they didn't in the 1940s. History hasn't been taught in our schools for about 40 years, so that's several generations of impaired high school and college graduates.