The subscription cancellations were coming every 10 minutes. Angry readers have been calling in droves. One caller issued a death threat.

“We’re feeling the weight of our history,” Phil Boas, the editorial page editor of The Arizona Republic, said in a telephone interview on Wednesday. Until it endorsed Hillary Clinton on Tuesday, the newspaper, founded in 1890, had never endorsed a Democrat over a Republican for president.

In endorsing Mrs. Clinton, The Republic’s editorial was, by any interpretation, scathing toward her opponent, Donald J. Trump. “Trump responds to criticism with the petulance of verbal spit wads,” the editorial says at one point. “That’s beneath our national dignity.”

“Trump’s long history of objectifying women and his demeaning comments about women during the campaign are not just good-old-boy gaffes,” the editorial added. “They are evidence of deep character flaws. They are part of a pattern.”