Some managers have been continually talking about politics in the office, not taking into consideration anyone else's political backgrounds and beliefs. It gets offensive at times, but employees are afraid to say anything. How should you handle it?
In general, a private employer can limit political expression in the workplace—provided they don't run afoul of protected Section 7 rights or applicable state laws. Section 7 of the National Labor Relations Act gives non-supervisory employees the right to talk about the terms and conditions of their employment and the right to unionize. While this law protects some political activities, it doesn’t give employees the right to discuss politics that aren’t work-related during work hours. You therefore can limit political speech and associated conduct that is not work-related.
As a rule, it is important to focus on workplace behavior and not on limiting the beliefs or off-work activities of employees. I recommend having workplace policies that focus on job performance rather than political discussions specifically. If an employee spends too much time engaged in "extra office chat," regardless of the topic, I'd presume that they are not performing their position to your expectations, or that they may be significantly distracting their co-workers.
As for how to specifically deal with this situation, I would recommend meeting privately with the managers involved and discussing with them how their comments are affecting the team. I would make it clear that you're in no way interested in limiting their political actions outside of work, but that it's important in the office to consider diverse views. Managers are held to a higher standard and should not be saying things that make subordinates feel uncomfortable.