The Union-Tribune isn't even the first conservative newspaper to break ranks in the past week. On Wednesday, the Arizona Republic (formerly, the Arizona Republican), tweeted out a photo of Clinton gazing into the distance while announcing its endorsement.
The editorials read less like ringing endorsements for Clinton than a repudiation of Trump. They're less "I'm with her" and more "I'm definitely not with him."
The Union-Tribune's editorial, for example, mentions Trump 11 times — and Clinton just three.
"Upon inauguration on Jan. 20, he would be in charge of the executive branch of a global superpower and possess enormous authority, operating with no coherent worldview besides 'I alone can fix it.'"
Later, the editorial tells readers: "Imagine that. Imagine President Trump."
The Tribune used to be locally owned. In 2015, it was bought by Tribune Publishing, which later changed its name to Tronc. Tronc also owns the nearby Los Angeles Times, as well as the Chicago Tribune.
The Republic's stance was similar. For 126 years, it had endorsed conservatives, but its editorial said Trump is not one.
"This year is different," the editorial board wrote. "The 2016 Republican candidate is not conservative and he is not qualified."
The latest endorsements echoed the scathing criticisms of Trump that appeared earlier in September.
The Dallas Morning News, whose editorial board had picked a Republican each time since before World War II, said Trump "plays on fear — exploiting base instincts of xenophobia, racism and misogyny — to bring out the worst in all of us, rather than the best."
The Cincinnati Enquirer, which had endorsed Republicans for nearly a century, called Trump "a clear and present danger to our country. ...Our reservations about Clinton pale in comparison to our fears about Trump."
The Houston Chronicle's editorial board called Trump "a danger to the Republic" and said his "convention-speech comment, 'I alone can fix it,' should make every American shudder."
USA Today has never endorsed a candidate for president, but its editorial board laid out eight reasons that people shouldn't vote for him.
No. 7: "He has coarsened the national dialogue. Did you ever imagine that a presidential candidate would discuss the size of his genitalia during a nationally televised Republican debate? Neither did we."
So far, Trump has racked up zero major newspaper endorsements. That's six fewer than Gary Johnson, who couldn't name any foreign leader he admires in an interview last week and about whom CNN opined "Why is Gary Johnson still in the race?"
Trump, for his part, has responded to these conservative defections on Twitter, saying that the papers are wrong and that their readers are smart people who will stop reading them.
The people are really smart in cancelling subscriptions to the Dallas & Arizona papers & now USA Today will lose readers! The people get it!— Donald J. Trump (@realDonaldTrump) September 30, 2016
Some readers told the papers the same thing.
Phil Boas, who runs the Arizona Republic's editorial board, told NBC-affiliate KPNX that "countless" newspaper readers have canceled their subscriptions. Others have sent death threats.