You can't discriminate against Trump supporters who just want to buy, say, a birthday cake. You can discriminate against Trump supporters who want to buy a cake for a Trump rally. At least that's my view. This is analagous to the gay wedding scenario.
Yeah you can tell a Trump supporter to leave your store if you want. You could even do the whole "we dont serve yer kind 'ere" shtick. In some places, however, orientation is not a protected class and LGBTQ people do face this type of discrimination. It is for that reason many feel principled law suits are very much in order when they are in an area where the law provides for orientation as a protected class.
The irony is, if people did not and had not continually discriminated against people based on orientation then orientation wouldn't be a protected class and people could discriminate based on orientation when it came to contributing services towards same sex weddings. But that wasn't the choice that was made. Many people vented and some continue to vent their hatred towards people based on their sexual orientation.
I fail to see why it is a big issue for the people being compelled to provide services. While this case is unique in that it brings up potential free speech issues, the real reason that people seem to be upset is that they believe they are being forced to contribute something to a same-sex wedding. Frankly, I see no issue there. We are dealing with state laws. States certainly have the right to dictate how business is conducted in their state. So where is the problem?