Usually, there has to be a reason for the clerk to ask a person to leave, ie; disorderly conduct, disturbance, something that would be detrimental to the business.
I doubt he could refuse service to someone just because he disagrees with the customer’s political views. Even though the Trump supporter is not a “protected class”, the business is open to the public and the clerk was way out of line.
Usually, there has to be a reason for the clerk to ask a person to leave
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It’s private property for crying out loud! Has this site been hacked tonight?
Political beliefs is definitely a protected class.