The US Supreme court ruled the other way as recently as 1989: https://en.wikipedia.org/wiki/Texas_v._Johnson

It was 5-4, but the majority included the venerable Justice Scalia.

How do we reconcile past SCOTUS decisions, and the pretty plain wording of the constitution's first amendment, with Mr Trump's decision? I mean, we as a country have been pretty happy with his decisions in other hotly contested matters. I supposed we can be happy with this one.