I see several major differences in the "Baker case" & what happened to Sarah.
First, the baker never refused to serve the gay couple outright, ie. he sold them many other products over many years & never refused them service or threw them out of his establishment. It wasn't until their was a religious issue, which is protected under law, that the baker very kindly explained why he was unable to participate in baking the wedding cake BUT went on to say that he would happily continue to bake other confections for the gay couple.
Secondly, as noted above, the baker's refusal was based on a religious, therefore protected, belief…not on a political belief.
In Sarah's case, she was refused service of ANY kind AND asked to leave the premises. Secondly, their is no religious basis for him to do either of those things and a difference in political beliefs as a basis for discrimination is not a protected belief.
That said, it could easily be argued that Dems are promoting a culture where we have Dem only restaurants & Conservative only restaurants. From there, it's not a very far journey to returning to the days of whites only, blacks only…..and it will be this move by a Liberal restaurant owner that starts the journey.