Political beliefs aren't protected in most states. In fact, I think California is the ONLY state where firing someone for political beliefs is prohibited:

https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=LAB§ionNum=1101

If anyone knows of another state with a similar law, please cite the law.

If you are the member of a protected class under federal law (gender, race, ethnicity, etc.), you can certainly sue if you are fired for that. But, employers know this, and will never say that was their reason. The burden is on the employee to prove it, and that's very difficult in the absence of evidence.

Spez: A tongue-in-check look at discrimination law:

A Halloween Guide – What Types of Monsters Are Protected from Discrimination?

Political beliefs aren't protected in most states. In fact, I think California is the ONLY state where firing someone for political beliefs is prohibited:

https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=LAB§ionNum=1101

If anyone knows of another state with a similar law, please cite the law.

If you are the member of a protected class under federal law (gender, race, ethnicity, etc.), you can certainly sue if you are fired for that. But, employers know this, and will never say that was their reason. The burden is on the employee to prove it, and that's very difficult in the absence of evidence.