Can you be fired for talking politics at work? Not necessarily. There are a couple of states (notably, California) that prohibit it. And if you work for the government, have a contract or are a union member, this doesn't apply to you.
But the majority of Americans employed in the private sector work "at will." According to law professor emeritus Joseph Little at the University of Florida, that means you are free to leave at any time, for any reason. That gives your boss a lot of latitude, too.
"An employer may fire the employee at will," Little said, adding, "For any reason. With no consequences."
Some of that pressure may be subtle, but in some cases it's explicit.
"I had a man within the last year tell me that he would fire any employee who voted the wrong way," Little said.
And unlike specially protected status like race or gender, if your boss fires you because of your politics, there's not a whole lot you can do about it.
"Under these circumstances, I think the employee has very little recourse," Little said, "Except, perhaps if the employer presses about how to vote: forget who you voted for."
That gets to the heart of the issue. Pressure in the workplace, if any, is likely to be subtle, but could have a measurable impact on how (and to what extent) you express yourself.
"My guess is that employees at will would be very reluctant to show their support for the opposing candidate," Little said.