WASHINGTON — President Trump called on Attorney General Jeff Sessions on Wednesday to end the special counsel’s inquiry into Russia’s interference in the 2016 election, issuing an unambiguous directive on Twitter to shut down an investigation that even now is scrutinizing his tweets for evidence of obstruction.

The White House and Mr. Trump’s lawyers moved quickly to minimize the president’s statement, dismissing it as merely a case of venting by a president who has grown increasingly angry with an investigation that he considers illegitimate — and not a direct order to a cabinet secretary to interfere with a continuing federal law enforcement matter.

But in saying that Mr. Sessions, the United States’ top law enforcement official, should take specific action to terminate the investigation, the tweet crossed a line that Mr. Trump has never explicitly crossed — until now. It immediately raised more questions about whether Mr. Trump was attempting to obstruct justice, already an issue being examined extensively by Robert S. Mueller III, the special counsel leading the investigation.

The trial of Paul Manafort, Mr. Trump’s former campaign chairman, which entered its second day Tuesday, has made the stakes of Mr. Mueller’s investigation increasingly clear. And even as Mr. Trump was calling for the investigation to end, it was revealed that he had pushed his lawyers to make another attempt to reach an agreement to sit for an interview, an objective that the president has long sought because of his belief that he can convince Mr. Mueller of his version of events.