Donald Trump promised to bring the country together, and he’s finally accomplished it. On Thursday, people from across the political spectrum were unified in their condemnation of his incredibly crass and sexist attack on Mika Brzezinski, the co-host of MSNBC’s “Morning Joe.”

In a pair of tweets he posted from the White House just before 9 A.M., Trump wrote, “I heard poorly rated @Morning_Joe speaks badly of me (don't watch anymore). Then how come low I.Q. Crazy Mika, along with Psycho Joe, came to . . . to Mar-a-Lago 3 nights in a row around New Year’s Eve, and insisted on joining me. She was bleeding badly from a face-lift. I said no!”

The criticisms of Trump began to pour in almost immediately, and some came from senior Republicans. “Mr. President, your tweet was beneath the office and represents what is wrong with American politics, not the greatness of America,” Senator Lindsey Graham, of South Carolina, wrote, on his own Twitter account. Senator Ben Sasse, of Nebraska, tweeted, “Please just stop. This isn’t normal and it’s beneath the dignity of your office.”

Graham and Sasse have both criticized Trump before. This time, though, some political allies of Trump, including Paul Ryan, the Speaker of the House, joined them. “Obviously, I don’t see that as an appropriate comment,” he said at a press conference on Capitol Hill. “What we’re trying to do around here is improve the tone and civility of the debate, and this, obviously, doesn’t help do that.”

Brzezinski herself responded by posting a picture of a Cheerios box that featured the words “Made for Little Hands”—a snickering reference to a longtime Trump insecurity. But perhaps the most fitting riposte came from Mark Kornblau, a spokesperson for NBC. “Never imagined a day when I would think to myself, it is beneath my dignity to respond to the President of the United States,” Kornblau wrote on Twitter.

Apart from a few members of the pro-Trump echo chamber, such as Sean Hannity, practically the only people defending Trump were members of his communications team. Sarah Huckabee Sanders, a White House spokesperson, told Fox News that Brzezinski and Scarborough had made “hateful attacks” on Trump, and, she added, “This is a President who fights fire with fire.”

Trump has made sexist and misogynistic remarks before, of course. His attacks on Megyn Kelly and Carly Fiorina during the Presidential campaign come to mind, and so does the infamous “Access Hollywood” tape, in which he was recorded boasting about sexually assaulting women. But Trump is no longer merely a reality-television star or a political candidate. He’s been in the Oval Office for more than five months now.

“This is not okay,” Lynn Jenkins, a Republican congresswoman from Kansas, wrote on Twitter. “As a female in politics I am often criticized for my looks. We should be working to empower women.” The Republican senators Susan Collins and Lisa Murkowski, who sat near Trump at a White House meeting about health care just a couple of days ago, both avoided publicly calling Trump a sexist jerk. But they did say that this sort of behavior had to stop, and Murkowski added, “@POTUS, do you want to be remembered for your tweets or your accomplishments?”

Actually, that is an interesting question. Trump’s online presence isn’t something incidental to his Presidency: it is central to it, and always has been. If the media world were still dominated by the major broadcast networks and a handful of big newspapers, Trump would most likely still be hawking expensive apartments, building golf courses, and playing himself in a reality-television series. It was the rise of social media, together with the proliferation of alternative right-wing news sites, that enabled Trump to build a movement of angry, alienated voters and, ultimately, go from carnival barker to President.

Trump is well aware of this fact. “I really believe that the fact that I have such power in terms of numbers with Facebook, Twitter, Instagram, et cetera, I think it helped me win all of these races where they’re spending much more money than I spent,” he told CBS News’s Lesley Stahl a week after the election. “I think that social media has more power than the money they spent, and I think maybe, to a certain extent, I proved that.” Whenever somebody, Democrat or Republican, suggests that Trump should give his Twitter finger a rest, he suspects that a nefarious plot is afoot to rob him of his most powerful tool. “I’m not saying I love it, but it does get the word out,” he told Stahl. “When you give me a bad story . . . I have a method of fighting back.”

He has relied as heavily on Twitter while in the White House as he did during his campaign, especially as the story of the Russia investigation has developed. Since late last week, when CNN retracted a story that said the Senate Intelligence Committee was investigating the Russian ties of one of his associates, the Wall Street financier Anthony Scaramucci, Trump has been ranting at the “FAKE NEWS” media on a daily basis. “So they caught Fake News CNN cold, but what about NBC, CBS & ABC? What about the failing @nytimes & @washingtonpost? They are all Fake News,” Trump tweeted on Tuesday. On Wednesday, he was back at it: “The failing @nytimes writes false story after false story about me. They don’t even call to verify the facts of a story. A Fake News Joke!” And, a bit later: “The #AmazonWashingtonPost, sometimes referred to as the guardian of Amazon not paying internet taxes (which they should) is FAKE NEWS!”

The substance of these messages was paper-thin. (The Times routinely checks with the White House before publishing stories; Amazon has collected state sales taxes for years.) In some quarters, there was speculation that Trump was attacking the Times and the Post because he knew they were working on stories containing additional damaging revelations. But it is also perfectly possible that he was just venting. According to any number of inside-the-White House stories, Trump’s default state of mind now is one of thinly controlled rage at the news media. Firing broadsides on Twitter is how he releases some of that anger.

The attack on Brzezinski seems to have been motivated by pure spite. Although “Morning Joe” is widely watched inside the political world, it doesn’t have a mass audience, and it doesn’t do much investigative journalism. As such, the show represents a source of irritation more than a serious danger to Trump. But he appears to be furious about the fact that Brzezinski and Joe Scarborough, her co-host, have joined the ranks of his critics after courting him for interviews during the election and transition—a courtship that included a visit the pair made to Mar-a-Lago on New Year’s Eve.

Although Trump claimed that he no longer watches “Morning Joe,” the timing of his tweets suggests otherwise. On Thursday’s show, according to a report by the Washington Post, Brzezinski mused aloud about what would happen if someone “took over NBC and started tweeting wildly about people’s appearances, bullying people, talking about people in the competition, lying every day, undermining his managers, throwing them under—the person would be thrown out. It’s just not normal behavior. In fact, there would be concern that perhaps the person who runs the company is out of his mind.”

This was not a flattering peroration, certainly. But Brzezinski was only saying what others, including me, have said before: if Trump were a corporate C.E.O., he would have been fired by now. Brzezinski also wasn’t the first to suggest that Trump may be losing his marbles: at water coolers and bars across the country, this is an everyday topic of conversation. But Presidents are supposed to rise above such speculation and chitchat.

Back in November, when Trump spoke to Stahl, he said that he would probably keep using Twitter after he took office, but he also intimated that he would tone things down. “I’m going to do very restrained, if I use it at all,” he said. This is turning out to be one of his many unfulfilled promises. And Thursday’s outburst confirmed a sad truth. Where America, until recently, had at its helm a Commander-in-Chief whom other countries acknowledged as a global leader and a figure of stature even if they didn't like his policies, it now has something very different: an oafish Troll-in-Chief who sullies his office daily.