JOHNSTOWN, Pennsylvania — When Ken Miller changed his party registration from Democrat to Republican in September 2020, he said he wasn’t doing it for Donald Trump. He had not voted for Trump or Hillary Clinton in 2016. Rather, he said, he was doing it for himself and his community after watching Democrats govern during the pandemic.

“I am tired of what I am seeing,” he said. Democrats appeared to ignore people like Miller, viewing his vote as replaceable by someone in their theoretical ascendant Democratic coalition of young people, women, intellectuals, and nonwhite voters. But the thinkers in Washington may have been too clever by half.