NEW YORK — President Trump said Saturday that he is not worried about what former national security adviser Michael Flynn might share now that he is cooperating with prosecutors, forcefully asserting that there was “absolutely no collusion” between his campaign and Russia.

On a day Trump spent here largely being whisked among political fundraising events, he both talked to reporters and took to Twitter to weigh in on the case of Flynn, who pleaded guilty Friday to lying to the FBI about his interactions with a Russian official.

A tweet posted Saturday afternoon by the president suggested that Flynn’s misstatements to the FBI were part of the rationale for Trump’s firing him 25 days into the new administration — something the White House had never asserted before and that some observers speculated could be legally problematic for Trump. The tweet was drafted by one of the president’s lawyers, however, according to two people familiar with the communication.

Flynn’s decision to cooperate with special counsel Robert S. Mueller III was widely seen as a sign of increasing legal peril for other White House aides and perhaps Trump himself, as the investigation has expanded beyond potential collusion with Russia to include obstruction of justice and financial crimes.

Asked by a reporter as he left the White House on Saturday morning whether he was worried about what Flynn might tell prosecutors, Trump said: “No, I’m not. And what has been shown is no collusion. No collusion. There has been absolutely no collusion. So we’re very happy.”

Later in the day, while traveling in his motorcade between fundraisers to benefit his reelection campaign and the Republican National Committee, the president tweeted that he thought Flynn’s lies were a “shame,” given that the former adviser’s underlying actions were “lawful” and that he had had “nothing to hide.”

Flynn, who had been one of Trump’s closest and most-trusted aides during the campaign and transition, admitted lying to the FBI about pre-inauguration communications with Sergey Kislyak, then the Russian ambassador, regarding efforts to blunt the Obama administration’s Russia sanctions and a U.N. resolution on Israel — potential violations of a rarely enforced law.

In the president’s Saturday afternoon tweet, he also added to his previously stated rationale for firing Flynn. Trump said that Flynn had been dismissed not only for misleading Vice President Pence about the nature of his conversations with Kislyak but also for lying to the FBI.

“I had to fire General Flynn because he lied to the Vice President and the FBI,” Trump said in the tweet.

Trump lawyer John Dowd drafted the president’s tweet, according to two people familiar with the message. Its authorship could reduce how significantly it communicates anything about when the president knew that Flynn had lied to the FBI, but it also raises questions about the public relations strategy of the president’s chief lawyer.

Two people close to the administration described the tweet simply as sloppy and unfortunate.

Several legal observers suggested that the tweet could add to Trump’s legal exposure in a potential obstruction-of-justice investigation.

The day after Trump fired Flynn, Trump urged then-FBI Director James B. Comey to be lenient with his former national security adviser, according to Comey’s notes at the time.

If Trump knew at that point that Flynn had lied to the FBI and was under investigation, the observers said, his appeal to Comey could constitute an attempt by Trump to obstruct that investigation.

“Are you ADMITTING you knew Flynn had lied to the FBI when you asked Comey to back off Flynn?” Walter Shaub, the former head of the U.S. Office of Government Ethics, said in a tweet Saturday afternoon.

Dowd declined to answer questions about how and when Trump learned of Flynn’s alleged lies to the FBI, a deception that did not become public until several days after Flynn’s dismissal.

“The tweet just paraphrases what Ty Cobb issued yesterday,” Dowd said in an email, referring to a statement issued by another lawyer for Trump in response to Flynn’s guilty plea.

Cobb’s statement Friday said that the misstatements to which Flynn pleaded guilty “mirror the false statements to White House officials.”

The president continued tweeting about Flynn on Saturday night. In one message, he complained that it was unfair for Flynn’s life to be “destroyed” for lying to the FBI, arguing that the agency pursued Democrat Hillary Clinton far less aggressively while investigating her use of a private email server as secretary of state.

In another post, Trump congratulated ABC News for suspending investigative reporter Brian Ross for an erroneous story about Flynn.

Trump’s lawyers have begged him not to tweet about Russia or the investigation, but the president said repeatedly Friday that he wanted to respond to the Flynn news, associates said.

Cobb has told others that he has been more successful than others at limiting Trump’s tweets because he talks to him frequently and reassures him

Meanwhile, an email written by a Flynn deputy that came to light Saturday suggests that many of Trump’s closest aides were informed that Flynn planned to discuss sanctions with the Russian ambassador before Flynn made a December phone call to Kislyak.

The email was written by K.T. McFarland, who at the time had been tapped to serve as deputy national security adviser and has now been nominated to be the U.S. ambassador to Singapore. In the Dec. 29 email, which was described to The Washington Post by two people who have seen it, McFarland characterized new sanctions imposed against Russia by President Barack Obama as an attack against the legitimacy of Trump’s election that could hurt Trump’s efforts to work with Russia.

McFarland indicated that Flynn planned to discuss the issue with Kislyak.

The email was sent to a number of Trump’s transition aides, including incoming White House chief of staff Reince Priebus and adviser Stephen K. Bannon.

The email was obtained in full by the New York Times, which first reported on its content. According to the Times, McFarland wrote the email to one transition official, who forwarded it to six others.

In the email, McFarland wrote about her fears that the Obama administration sanctions could interfere with Trump’s hope to improve relations with Russia, “which has just thrown the U.S.A. election to him,” the Times reported.

The Times said it was unclear if McFarland meant that she believed Russia had thrown the election to Trump, and a White House lawyer told the newspaper that McFarland was describing the view of many Democrats.

Despite the emails, Sean Spicer, Trump’s White House press secretary at the time, and Priebus both publicly denied that Flynn had discussed sanctions during his communications with Kislyak, as did Pence.

Bannon declined to comment about the email, as did Cobb. McFarland did not respond to a request for comment.

William Burck, an attorney for Priebus, said in a written statement that Priebus “does not remember this email, either because he didn’t receive it (it was sent to an account he rarely, if ever, used) or he didn’t see it.”

Burck said that Priebus “confronted General Flynn several times, including in front of others, on whether he had talked to Kislyak about sanctions and was consistently told he had not.”

The email provides more evidence that top Trump advisers were notified that Flynn planned to raise the sanctions issue with Kislyak.

Court documents filed Friday show that Flynn discussed the matter with a senior Trump official who had accompanied the president-elect on a trip to Trump’s private Mar-a-Lago Club. The senior official was McFarland, according to two people familiar with the conversation.

Despite the continued media focus on Flynn, Trump was in a buoyant mood as he crossed Manhattan on Saturday, bragging about his election win in Rust Belt states and the improving economy. He did not mention Russia or Flynn, attendees of the various fundraisers said.

At several stops, he touted the Senate’s passage of the GOP tax bill and predicted that Democrats who voted against it would lose their next elections.

Trump’s stops included the palatial Upper East Side apartment of Steve Schwarzman, chairman of a global private-equity firm.

Trump said he understood criticism from New Yorkers about one of the bill’s provisions, which would curb the ability of filers to claim deductions for state and local taxes. Residents of New York and other relatively high-tax states would be hit hardest.

Trump also told the wealthy donors at the event that the legislation was for the middle class and urged people to call members of Congress to make sure the House and Senate reconcile their respective versions of the bill.

Trump said he expects Congress to make a deal but did not offer many specifics on what he wanted to see, “other than a quick deal,” according to one person with knowledge of his remarks.

Trump also praised his relationship with China’s president but said China still needs to do more to address the nuclear threat posed by North Korea.

At another fundraiser, at the restaurant Cipriani, Trump brought White House counselor Kellyanne Conway on stage to make a presentation about polling. She made the case that Trump is politically strongly positioned.

Carol D. Leonnig, Aaron Blake and Ashley Parker contributed to this report.