WASHINGTON — It was supposed to be a quiet, private day for President Donald Trump, with no public events listed on his schedule.

Instead, using the virtual slingshot of Twitter, the president launched a fusillade of grievances, insults, boasts and denials from inside the fortress at 1600 Pennsylvania Avenue. In addition to the tweets, Trump gave wide-ranging interviews to the Associated Press and the Fox Business Network, further demonstrating his ability to completely dominate news cycles without appearing in public.

"Horseface," "Pocahontas," "witch hunt," Trump said in some of the dozen tweets he sent out before noon Tuesday.

Later in the day, and on a more serious and controversial note, Trump sent two tweets informing the world that Crown Prince Mohammad bin Salman, the de facto ruler of Saudi Arabia, had "totally denied any knowledge" of the disappearance of Washington Post journalist Jamal Khashoggi from his country's consulate in Turkey — even though Republican senators have been saying for days that they believe bin Salman had Khashoggi murdered.

To the president's fans, heavy bursts like these — which have become familiar, if not exactly regular — are a reminder that the president is on the job, ready at all times to protect allies and fight adversaries. To his critics, they're evidence that he's unhinged.

Theories abound: Maybe he's just bored when he doesn't have a campaign rally, a meeting with a foreign leader or a bill-signing ceremony on the docket, or perhaps he doesn't like to be outside the center of national attention for very long.

The motivation and the strategy may be a mystery even to those closest to him — or at least, they appear reluctant to talk about his penchant for talk: Several current and former White House officials did not respond to NBC requests for comment on what prompts the president to turn a ho-hum day in the West Wing into a hullabaloo on social media.

Trump started his day on predictable turf, tossing taunts at Sen. Elizabeth Warren, D-Mass., who on Monday released DNA evidence showing she almost certainly has some small fraction of Native American ancestry. Trump, mocking her claims of that heritage, calls her "Pocahontas," and Republicans — and some Democrats — were quick to argue that the DNA tests actually made her use of Native American heritage on job forms look worse.

Pocahontas (the bad version), sometimes referred to as Elizabeth Warren, is getting slammed. She took a bogus DNA test and it showed that she may be 1/1024, far less than the average American. Now Cherokee Nation denies her, “DNA test is useless.” Even they don’t want her. Phony! — Donald J. Trump (@realDonaldTrump) October 16, 2018

In the second of three tweets on the subject, Trump, who had promised earlier this year to give $1 million to the charity of Warren's choice if she could prove she is "an Indian," said Warren "should apologize for perpetrating this fraud" on the American people.

From there, he moved on to immigration, threatening to cut off foreign aid to Honduras if a caravan of immigrants crosses the U.S. border — even though he would need Congress to do that — and citing a Washington Examiner op-ed praising him for trying to prevent unaccompanied minors who cross the U.S. border from being released to criminals.

Then, he mixed and matched themes.

He touted Charles V. Payne's analysis on Fox News stating that there are eight times as many new manufacturing jobs in the U.S. under Trump than President Barack Obama — the number of manufacturing jobs now is about 1.5 percent higher than it was during Obama's last full month in office.

He argued that his response to the Khashoggi case has not been colored by his business dealings because, he said, he has no financial interests in Saudi Arabia (or, for that matter, Russia).

For the record, I have no financial interests in Saudi Arabia (or Russia, for that matter). Any suggestion that I have is just more FAKE NEWS (of which there is plenty)! — Donald J. Trump (@realDonaldTrump) October 16, 2018

In the past, Trump has bragged about the profits he's made from deals with the Saudi government and Saudi citizens.

And then, before two messages about "the witch hunt" — his description of special counsel Robert Mueller's investigation into whether Trump or his allies colluded with Russia during the 2016 election or obstructed justice afterward — Trump took on Stormy Daniels, the pornographic actress who was paid $130,000 to keep quiet about her allegations that they had an affair.

"Horseface," he called his alleged ex-girlfriend, saying "she knows nothing about me."

“Federal Judge throws out Stormy Danials lawsuit versus Trump. Trump is entitled to full legal fees.” @FoxNews Great, now I can go after Horseface and her 3rd rate lawyer in the Great State of Texas. She will confirm the letter she signed! She knows nothing about me, a total con! — Donald J. Trump (@realDonaldTrump) October 16, 2018

Daniels responded with a Tweet calling Trump "Tiny."

Eventually, Trump started tweeting about the midterm elections, the subject that has the political class in Washington transfixed.

With just three weeks until voters go to the polls, he mixed in a few notes on electoral politics. He retweeted one of son Eric Trump's requests for supporters to register to vote and proclaimed that John James, the Republican Senate candidate in Michigan, is ascendant based on polls showing a narrowing of the gap between him and Sen. Debbie Stabenow, a Democrat who has been above 50 percent in every public survey.

By the end of the business day, Trump had tapped out 16 tweets covering a vast array of topics and individuals, but with one overriding focus: Himself.

CORRECTION (11:17 p.m. ET): An earlier version of this article misstated the name of the cable channel President Donald Trump appeared on Tuesday. It was Fox Business Network, not Fox Business channel.