You would likely lose.
Look at the bakers and photographers who would not serve gay weddings.
Those states had laws saying you cannot discriminate based on sexual orientation. Unless the state includes political belief as a protected class then you are going to lose.
It’s totally a Freedom of Speech issue.
By the wearing of those shirts and hats, they were exercising their constitutionally protected right to campaign/”speak” for their candidate.
Would they have been so treated had their worn “Vote for the tax increase for the new animal shelter?” Of course not.
Remember, at law, Constitutionally protected speech is far beyond just the spoken word.