The attorney for Donald Trump says the president pardoning himself would be unthinkable and probably lead to immediate impeachment

Rudy Giuliani has backed claims made in a newly leaked memo from Donald Trump’s legal team that the president can’t be compelled to testify by a grand jury subpoena as part of the Russia investigation.

That question was posed on Saturday when the New York Times published a January-dated letter from Trump’s lawyers to special counsel Robert Mueller, which argued that Trump could “if he wished, terminate the inquiry, or even exercise his power to pardon”.

Asked if that meant Trump has the power to pardon himself, the president’s attorney remarked that he “probably does”. But the political ramifications, Giuliani added, “would be tough. Pardoning other people is one thing. Pardoning yourself is another.”

Ultimately, Giuliani told NBC’s Meet the Press, he thought Trump pardoning himself would be “unthinkable and probably lead to immediate impeachment”.

He added: “He has no need to do it, he’s done nothing wrong.”

Giuliani said he would be “willing to sit down with Mueller and argue it out if he has an open mind to it”.

The former New York Mayor and mob prosecutor has taken a leading role in defending Trump, sometimes with conflicting statements that get information out there but also making it appear accidental or disinformation.

On Thursday, Trump said that he is considering pardoning Martha Stewart, the home decorating mogul who served five months in prison for obstructing justice and similar charges as part of a 2004 insider trading investigation. Trump is also mulling whether to pardon the former Illinois governor Rod Blagojevich.

With the notion of pardoning the pair, many interpreted as a signal to allies ensnared in the Russia probe but also to raise the topic of how widely the president – any president – can use the executive office’s pardoning power.

But Giuliani also appeared to want it known that if Trump used his power to pardon himself, and triggered a constitutional crisis, it would be in vain since there had been no obstruction of justice in the first place.

“He [Trump] has broad constitutional powers and somebody who wants to question that has a big burden to show there is no explanation for what he did. I would like to caution them to exercise constitutional restraint here.”

Giuliani said he doubted Trump would now grant Mueller an interview.

“I mean, we’re leaning toward not,” Giuliani told ABC. “But look, if they can convince us that it will be brief, it would be to the point, there were five or six points they have to clarify, and with that, we can get this – this long nightmare for the … for the American public … over.”

Giuliani also on Sunday backed Donald Trump Jr, who had arranged a meeting at Trump Tower in Manhattan with Russian lawyer Natalia Veselnitskaya, who has connections to the Kremlin, soon after clinching the Republican presidential nomination in 2016.

On Saturday, the letter by Trump’s lawyersacknowledged for the first time that the president had dictated a statement about his son’s meeting, which also involved Jared Kushner and former campaign manager Paul Manafort, and is believed to be part of Mueller’s reasoning for looking at a cover-up involving Trump over the extent to which his campaign was working with Russia.

Trump’s lawyers and the White House press secretary Sarah Sanders previously denied the president had dictated the statement and only offered suggestions.

On Sunday, Giuliani, by turns, said that conflicting statements about the source of Don Jr’s statement were one reason he would not want the president, his client, to grant an interview to Mueller’s prosecutors.

“I mean, this is the reason you don’t let the president testify,” he added.

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