Donald trump first admitted that his son met with a Kremlin-related lawyer in 2016 to gather information about Hillary Clinton, but insists that the meeting was legal.

In one of a series of Sunday morning tweets issued in apparent reaction to a CNN report, the US president wrote: “Fake News reporting, a complete fabrication, that I am concerned about the meeting my wonderful son, Donald, had in Trump Tower. This was a meeting to get information on an opponent, totally legal and done all the time in politics – and it went nowhere. I did not know about it!”

That explanation differs entirely from one given by Trump 13 months ago, when a statement dictated by the president but released under the name of Donald Trump Jr read: “We primarily discussed a program about the adoption of Russian children that was active and popular with American families years ago.”

The 2016 meeting is pivotal to the special counsel Robert Mueller’s Russia collusion investigation, though Trump’s tweets appeared aimed at conveying the message that he is not worried about Donald Trump Jr’s exposure to the inquiry.

He made the remarks as one of his lawyers warned the special counsel against trying to force the president to be interviewed.

Trump has launched a series of new public attacks on Mueller and his team in recent weeks, which has been interpreted as possible signs the president is anxious about the inquiry reaching his family.

Trump, who is currently ensconced at his Bedlington, New Jersey, golf course for an 11-day “working holiday”, has a decision to make over whether to sit for an interview with Mueller – or risk being issued a subpoena.

Trump’s legal team have gone back and forth on the issue, playing each scenario out in the court of public opinion to see how it plays.

On Sunday, a Trump lawyer, Jay Sekulow, told ABC News’ George Stephanopoulos that if Mueller subpoenas Trump to testify, it would spark a legal battle that would go to the supreme court.

“A subpoena for live testimony has never been tested in court as to the president of the United States,” Sekulow said.

In Trump’s early Sunday Twitter barrage, he again sought to link Mueller’s investigation with the motives of his political opponents, government law enforcement agencies and the media’s reporting of his presidency.

“Why aren’t Mueller and the 17 Angry Democrats looking at the meetings concerning the Fake Dossier and all of the lying that went on in the FBI and DOJ? This is the most one sided Witch Hunt in the history of our country. Fortunately, the facts are all coming out, and fast!”.

Trump Jr’s exposure to the Mueller investigation stems from a meeting with a Kremlin-connected Russian lawyer promising damaging information on Hillary Clinton that he and Trump son-in-law Jared Kushner attended at Trump Tower in July 2016.

Trump Jr’s claim to a Senate committee that he never told his father about the meeting have been contradicted by others in Trump’s circle, including Trump’s lawyer and fixer Michael Cohen, who is believed to be cooperating with the investigation.

The former White House communications director Anthony Scaramucci and the former White House chief strategist Steve Bannon have suggested that Trump, at a minimum, knew of the meeting soon after it took place.

Senior Republicans have sought to distance themselves from Trump’s attempt to protect Trump Jr by claiming he, too, is the victim of a witch-hunt, a phrase Trump has tweeted 46 times over the past two months in connection to Mueller.

In private, Trump reportedly believes his son may have inadvertently exposed himself to legal jeopardy.

Last week, the Iowa Republican Chuck Grassley, chairman of the Senate judiciary committee, told CNN: “If he misled the committee, he’s lying to Congress. That’s a crime. And that’d be up to the prosecutors, not me.”

Still, Trump’s concern for his son, and his efforts to protect him, speaks to a larger sense of frustration that is beginning to envelop the presidency. Trump is believed to be aggrieved by Mueller’s treatment of Paul Manafort, his former campaign chairman, who went on trial last week on tax evasion and bank fraud charges.

“He is completely outraged by the way Manafort has been treated, with the solitary confinement and all of that,” Trump’s legal counsel Rudy Giuliani told the Washington Post. “It’s obvious to him that they’re all but torturing Manafort in order to try to get him to flip.”

Last week, Trump called on his attorney general, Jeff Sessions, to end the investigation, a position White House communications staff had then to describe as “a personal opinion”.

“With his great feel for public opinion and how to deal with it, he has a sense about what would work, what to say,” Giuliani said this week. “He sort of determines the public strategy, and we get his approval and input for the legal strategy.”