The error message on some devices was even more dire: “@realDonaldTrump does not exist.”

Amid a presidency that has seemed, at times, to be conducted primarily in 140-character pieces, this was a seismic event — and what was left of Twitter erupted. It was a raucous, modern-day town-square gathering of the sort not seen since … well, since five months ago, when Mr. Trump coined a new word in the middle of the night.

It was just before 7 p.m. Thursday, and the internet was in an uproar. Time stopped. The sun rose in the west and set in the east. What, the watchers wondered, was going on? Had Twitter closed the president’s account? Had a White House aide snatched the phone from Mr. Trump’s tweeting hands? Had Robert Mueller chosen this moment to rifle through the president’s direct messages? Had Mr. Trump himself — could it be? — decided he’d had enough of his favorite medium?