Donald Trump has doubled-down on what he believes is his right to fire anyone who works for the government and blasted the Russia probe as a “witch hunt” – even as his lawyers prepare for a legal showdown with Robert Mueller.

Just weeks ago, the president claimed he was happy to sit down with the special prosecutor and answer any questions he had, as he believed the process would clear him of any suspicion of wrongdoing.

Yet, since the leaking of dozens of questions Mr Mueller apparently wants to put to the president, and after it emerged he had reportedly threatened to subpoena him if he was unwilling to talk, Mr Trump’s lawyers are now fighting even harder to avoid him sitting down with the special counsel.

Donald Trump and Emmanuel Macron plant tree at White House

On Wednesday, in the latest piece of political sabre-rattling, Mr Trump claimed he was being unfairly treated. “There was no collusion (it is a hoax) and there is no obstruction of justice (that is a set-up & trap). What there is is negotiations going on with North Korea over nuclear War, negotiations going on with China over trade deficits, negotiations on Nafta, and much more. Witch hunt,” he tweeted.

In a remark that was apparently directed at Mr Mueller, he quoted comments from former US attorney Joe Digenova, who had suggested the president had power under the constitution to fire “any executive branch employee”.

The prospect of Mr Trump being subpoenaed by the special council was apparently raised during a meeting between Mr Mueller’s team and the president’s lawyers in March.

Mr Trump’s former lawyer John Dowd confirmed to the Associated Press that the issue had been raised, but that it was not immediately clear in what context. It is known that Mr Mueller’s investigation into Russia’a alleged meddling in the 2016 election and possible collusion with the Trump campaign, is also looking at possible obstruction of justice by Mr Trump.

Indeed, Mr Mueller was only appointed to head a special investigation into the matter when Mr Trump fired FBI director James Comey after he became disgruntled with the direction the investigation was taking and described the director as a “showboat”.

Mr Comey has since responded in literary style, writing and publishing a best-selling memoir, A Higher Loyalty: Truth, Lies and Leadership, which has received media coverage and in which the former FBI chief claims Mr Trump is “morally unfit to be president” and that it was “possible” Russia has material it that could be used to blackmail him.

Eric M Freedman, professor of constitutional rights at New York’s Hofstra University, told The Independent Mr Mueller did have the constitutional right to subpoena the president, though he said historically such events had been largely been avoided.

The most recent cases, he said was the subpoena issued by special prosecutor Leon Jaworski against Richard Nixon in 1974, in order to obtain tape recordings and documents relating to the Watergate investigation. The White House refused, but the Supreme Court ruled in Mr Jaworski’s favour.

Meanwhile, in 1997, in Clinton v Jones, the Court directed Bill Clinton to comply with a subpoena for his deposition in Paula Jones’ civil sexual harassment lawsuit against him.

Asked what advice he might give Mr Trump’s lawyers, Mr Freedman said: “You can run, but you can’t hide.”

He said rather that seeking a legal showdown, he would do better to come to a deal on how he might respond to the special counsel’s questions, especially given that he had undertaken to do so. “The history of presidential scandals shows that the cover-up is usually more damaging than the actual incident,” he said.

Yet, it is far from clear, Mr Trump’s lawyers share that view. CNN said sources close to the president believed the chances of Mr Trump sitting for a voluntary interview with Mr Mueller’s investigators were “growing dimmer”. Asked whether the president would ever plead the fifth amendment to avoid answering questions, two sources said the legal team believed there are many “constitutional challenges” that would need to be met before that possibility even would be considered, the network said.

Reports suggest, Mr Trump’s view about the legitimacy of Mr Mueller’s probe took a “seismic shift”, after the New York offices of his personal lawyer, Michael Cohen, were raided on 9 April.

Mr Dowd’s comments come more than a month after he resigned from the legal team. The AP said they provide a new window into the nature of the Trump lawyers’ interactions with the special counsel, whom the president has increasingly tried to undermine through public attacks.

It is likely that attacks by Mr Trump and his supporters are likely to be stepped up, as part of a strategy to undermine Mr Mueller’s investigation, even before it it publishes its report.