WASHINGTON — There was a time in the not-too-distant past when President Trump refrained from flamethrowing messages on Twitter.

That time is over.

Never mind that his aides have asked him to stop. Never mind that the lawyers have told him to stop. Even though his White House has been warned that tweets could be used as evidence against him, Trump has made clear in the days after returning from a largely Twitter-free overseas trip that he fully intends to stick to his favorite means of communication. Since the weekend, he has gone after favorite targets, like the “fake news’’ media and Hillary Clinton, and some new ones, like Germany and comic Kathy Griffin. He denounced the “witch hunt’’ investigations into contacts between Russia and his associates.

And he fomented a worldwide mystery with a middle-of-the-night post that introduced a new word: “covfefe.’’

Throughout last year’s campaign and into the early months of his presidency, the concern among Trump’s advisers was mainly political. Every time the president let loose with one of his 140-character blasts, it distracted from his agenda and touched off a media frenzy that could last for days.

But now the worry has turned increasingly legal. With multiple investigations looking at whether the president’s associates collaborated with Russia to influence the election, any random, unfiltered tweet could become part of a legal case.

“There is a reason for the old lawyer’s proverb: The fish got hooked because it opened its mouth,’’ said Robert F. Bauer, a White House counsel under President Barack Obama.

“Tweeting spontaneous thoughts and feelings may be emotionally satisfying in the middle of the night, but Mr. Trump’s lawyers will surely remind him that there are always fishermen around, casting their lines.’’

More than ever, the White House is looking at the Russia case through a legal prism and hoping to wall it off from day-to-day governance. Aides are assembling a team of lawyers, including some who would join the staff and others who would remain outside the White House. Individual aides are also shopping for lawyers.

At his daily briefing Wednesday, where he took questions for just 7½ minutes, Sean Spicer, the White House press secretary, refused to address the Russia investigations, saying that from now on all such inquiries should go to Marc E. Kasowitz, the president’s personal lawyer. Kasowitz’s office, which was still setting up operations, had no comment.

Spicer offered no explanation for the president’s curious tweet, posted after midnight on Wednesday morning: “Despite the constant negative press covfefe.’’ It seemed likely he meant “coverage’’ and intended to say more, but social media users around the globe traded theories and jokes about the meaning of “covfefe.’’

Spicer seemed to suggest it was an inside joke or a kind of code. “The president and a small group of people know exactly what he meant,’’ he said in total seriousness and then refused to elaborate. Trump seemed amused by the attention and joked about it in a tweet when he woke up Wednesday. “Who can figure out the true meaning of ‘covfefe’???’’ he wrote. “Enjoy!’’

Every lawyer consulted by White House aides in recent days has made the same point about the president: He can power through investigations, but he is his own worst enemy if he continues to vent online. The lawyers noted that Trump’s words have already been used against him in court cases challenging his orders temporarily barring visitors from several predominantly Muslim countries. Judges cited his statements during the campaign.

Whether the same could be true in criminal proceedings was unclear, some lawyers said, asking why he’d take a chance.