Rod J. Rosenstein, the deputy attorney general, last month named Robert B. Mueller, a former F.B.I. director, as a special counsel to lead the sprawling investigation into the extent of Russia’s meddling in the 2016 presidential election, and whether any of Mr. Trump’s associates colluded in that effort.
In addition, two congressional committees have issued subpoenas for testimony and documents as part of their wide-ranging, bipartisan investigations. All three inquiries are reportedly examining whether Mr. Trump, as president, sought to impede the progress of the inquiries.
Mr. Sekulow repeatedly and forcefully denied that on Sunday, saying on CBS’s “Face the Nation” program that “the president has not been and is not under investigation,” and insisting that the administration had received no information from the special counsel’s office to think otherwise.
On CNN’s “State of the Union” program, he said flatly, “The president is not a subject or target of an investigation.”
On Friday, the president wrote the opposite on Twitter, saying: “I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt.”
Mr. Sekulow said that the message was merely a response by the president to a Washington Post article citing five unnamed sources who said Mr. Trump was under investigation in the Russia case. Mr. Sekulow said that Mr. Trump would have challenged the basic assertion of the article, but was constrained by Twitter’s limit of 140 characters per post.
“There’s a limitation on Twitter, as we all know,” Mr. Sekulow said on CNN. “And the president has a very effective utilization of social media.”
Mr. Sekulow did acknowledge on “Fox News Sunday” that he “can’t read people’s minds,” but said there had been “no notification of an investigation” of the president by Mr. Mueller.
“I can’t imagine a scenario where the president would not be aware of it,” Mr. Sekulow said on CBS.
Evidence that Mr. Mueller is in fact looking at Mr. Trump’s actions grew last week when Mr. Mueller requested interviews with three high-ranking current or former intelligence officials, according to a person briefed on the investigation. Reports have raised questions about whether Mr. Trump requested their help in trying to get James B. Comey, then the F.B.I. director, to end an investigation into the president’s former national security adviser, Michael T. Flynn.
Veteran lawyers who have represented presidents during high-stakes legal cases said Mr. Trump’s repeated comments about the Russia investigation were extremely unusual. They said previous presidents would make sure to have the White House counsel’s office and their personal lawyers carefully review any comments about such an investigation before making them.
They said Mr. Sekulow’s denials on Sunday were not so much a legal argument as an effort to repair the political damage from the apparent admission by Mr. Trump on Twitter.
“With all due respect to Mr. Sekulow, what he says about what Mr. Mueller is or isn’t doing will make no difference,” said Gregory B. Craig, who led the legal team defending President Bill Clinton against impeachment charges. “If Mueller thinks there is evidence that obstruction occurred, Mueller’s job is to investigate.”
Several lawyers who requested anonymity because they did not want to publicly comment on the president’s legal situation dismissed Mr. Sekulow’s comments about the president’s not having been notified that he is a target of the investigation. One noted that very few criminal investigations begin with an identified target. Rather, targets are notified much later, after evidence in the case is developed.
On Capitol Hill, members of both parties expressed exasperation with Mr. Trump’s continuing public commentary about the Russia investigation. Senator Marco Rubio, Republican of Florida, pleaded on Sunday for the president to give Mr. Mueller the room he needs to manage the inquiry.
“If I were the president, I would be welcoming this investigation,” Mr. Rubio said on CBS. “I would ask that it be thorough and completed expeditiously, and be very cooperative with it.”
Mr. Rubio added, “The best thing that can happen for the president and for America is that we have a full-scale investigation that is credible.”
Representative Adam Schiff, Democrat of California, accused Mr. Trump and his allies of seeking to undermine Mr. Mueller’s investigation, setting a pretext for potentially firing those leading it. Mr. Trump has reportedly told friends that he considered firing Mr. Mueller, and the president’s tweet on Friday appeared aimed at Mr. Rosenstein, raising questions about whether the president might fire him, too.
“What’s happening here is the president wants to take down Bob Mueller. His lawyer wants to take down Bob Mueller,” Mr. Schiff said on ABC’s “This Week” program. “They want to lay the foundation to discredit whatever Bob Mueller comes up with. They’re essentially engaging in a scorched-earth litigation strategy that is beginning with trying to discredit the prosecutor.”
During his five months as president, Mr. Trump has repeatedly made comments that administration officials later sought to correct or explain.
After Mr. Trump repeatedly called for a “Muslim ban” during the presidential campaign, White House aides and lawyers said the travel ban he imposed shortly after taking office was not aimed at any religious group. Federal judges, however, said they had looked to the president’s own statements as they assessed the constitutionality of the effort to impose a travel ban, a case that has reached the Supreme Court.
Just weeks after taking office, Mr. Trump told reporters that new immigration policies were getting rid of “really bad dudes” and added, “It’s a military operation.” John Kelly, the secretary of homeland security, quickly corrected: “No — repeat — no use of military force in immigration operations. None.”
On a Saturday morning in early March, the Mr. Trump accused former President Barack Obama of wiretapping, a charge that aides repeatedly struggled to explain. “I’m just going to let the tweet speak for itself,” Sean Spicer, the White House press secretary, said at the time. “I think the president speaks very candidly.”
In May, word leaked out that Mr. Trump had told Russian diplomats in the Oval Office that Mr. Comey was a “nut job,” and that his firing had relieved “great pressure” on the president. Lt. Gen. H. R. McMaster, his national security adviser, later went on television to say that “the gist of the conversation was that the president feels as if he is hamstrung in his ability to work with Russia to find areas of cooperation because this has been obviously so much in the news.”
And after a longtime friend of Mr. Trump said this month that the president was considering whether to fire Mr. Mueller, Sarah Huckabee Sanders, a spokeswoman, clarified his remarks during a gaggle with reporters on .
“While the president has the right to, he has no intention to do so,” she said.