YOUNGSTOWN, Ohio — In July 2017, just six months after President Donald Trump was inaugurated, he received a hero’s welcome for the ages in this post-industrial town. The streets took on a festival atmosphere as supporters, almost all dressed in some combination of red, white, and blue, clogged the arteries leading to the event center where he would be speaking.

People swayed to the music being played by several pop-up musicians, brandished hand-held American flags or homemade signs, and greeted newly formed acquaintances like long-lost friends.