It was further challenged when Preet Bharara, the much-admired US attorney of the southern district of New York, refused to comply with Donald Trump's request that he resign along with 45 other attorneys across the country who had been asked to quit, forcing the White House to sack him.

Bharara, whose current docket included investigations that threatened prominent Democrats such as New York state governor Andrew Cuomo and New York City mayor Bill de Blasio, had initially been asked by Trump to remain in the job.

But in his seven-year tenure as the district's chief law officer, Bharara became known as "the Sheriff of Wall Street" for fearless investigations into megabank JPMorgan Chase, Toyota and billionaire investor Steven Cohen. He was also investigating the handling by the Rupert Murdoch-owned Fox News of multimillion-dollar payouts to female staff who accused former Fox chief executive Roger Ailes of sexual harassment.

The administration's siege mentality risks becoming a permanent feature of the political landscape in Washington, with charge and countercharge at the weekend by Trump supporters and critics.

Presidential ally and Fox News talking head Sean Hannity urged Trump to "purge these saboteurs", telling his audience: "For months, deep state antagonists have been working overtime to try and delegitimise Donald Trump's presidency. One tactic has been to insinuate - without any evidence - that there was some sort of campaign collusion with Russia."

Democratic firebrand Elizabeth Warren shot back, tweeting to Trump: "You're not replacing real prosecutors with cronies without a massive fight."

Accusing Trump of "talking big" about getting rid of corruption, the Massachusetts senator charged that the President's real intent was to appoint "a bunch of tame prosecutors who won't investigate him".

But it was McCain who stopped Washington in its tracks with his bold insistence that Trump prove his claim that Obama tapped the phones in Trump Tower in Manhattan during last year's election campaign - or drop the accusation.

McCain told CNN's State of the Union: "The President has one of two choices, either retract or provide the information that the American people deserve. I have no reason to believe that the charge is true, but I also believe that the President of the United States could clear this up in a minute."

The 45th presidency has become enmeshed in vicious cycles, with Trump lashing out at government agencies, and the intelligence services in particular, which he accuses of Nazi-like criminal misconduct and incompetence in investigations that threaten him.

At the heart of it all is Trump's peculiar and unexplained fondness for Russia and the Kremlin's hacking intervention in last year's election campaign. These have spawned a torrent of leaks from the agencies and a countersurge of leaking by the administration, and more wild Twitter storms by Trump himself - such as his claim that Obama was eavesdropping on Trump headquarters - as well as his controversial chief strategist Stephen Bannon urging that Trump demolish what he calls an anti-Trump "administrative state".

McCain is hardly a deep-state activist. Similarly, his Republican Senate colleague Lindsey Graham is no subversive, but last week Graham joined forces with Democrat Sheldon Whitehouse to issue a bipartisan letter to FBI director James Comey asking that he provide "copies of any warrant applications and court orders - redacted as necessary ??? related to wiretaps of President Trump, the Trump Campaign, or Trump Tower" to the Senate judiciary committee.

"If the allegation is left out there, it undermines the confidence the American people have in the entire way that the government does business," McCain said on CNN, while another of his GOP colleagues, senator Roy Blunt, was telling Fox's Sunday Morning Futures that Trump had the authority to ask the FBI for the information that might corroborate his outlandish claim.

As with the Russia business, the sacking of Bharara is a peculiar, unexplained business.

Incoming presidents have often cleared out attorneys en masse; Bill Clinton did it early in his term and George W. Bush did it some time after becoming president, drawing flak by leaving himself open to the charge that the attorneys were asked to go because he didn't like how they operated.

But Trump, in a transition period meeting with Bharara that was attended by now Attorney-General Jeff Sessions, Bannon and Trump's son-in-law and counsellor Jared Kushner, expressly asked that Bharara remain in his post.

And there was a strange, unexplained phone call on Thursday - from the White House to Bharara's office.

A presidential aide reportedly asked for the attorney to call Trump, but Bharara explained strict protocols on communications between a president and a prosecutor made that impossible.

The only explanation by the White House, offered to The New York Times by administration officials who refused to be named, did cast the fate of a nominally independent attorney in a very political context; apparently the promise to retain Bharara had been made when Trump thought he might be able to have a working relationship with the leader of the Democrats in the Senate, Chuck Schumer, also of New York and close to Bharara.

But the Trump-Schumer relationship quickly soured and with that, Bharara's fate was sealed.

White House officials have denied that the purge of attorneys was a response by Trump to Hannity's call on Friday evening for a clean-out of what he described as "deep-state Obama holdovers embedded like barnacles in the federal bureaucracy [who] are hell-bent on destroying President Trump".

"Those who aren't actively working with President Trump to fix the country need to be shown the door. They are hurting the people who pay their salaries," he said.

Experts warn that leaks against Trump are organic, not organised. But they fear that in casting them as the work of a deep state, a term that usually refers to a civilian and military network who already control or are seeking to gut a democratically elected government, as in Turkey and Egypt, Trump's supporters run the risk of generating greater conflict, even more leaks and greater polarisation in government agencies.

Elizabeth Saunders, a George Washington University political scientist, warns that the administration is shooting itself in the foot, telling The New York Times that treating the bureaucracy as an adversary had served mainly to snare Trump in a controversy that made it more difficult to implement his policies.

"You get the feeling that Trump doesn't understand that working invisibly through the bureaucracy would strengthen him," Saunders said.

Saunders cites the politicisation of science in the climate change wars as a cautionary tale for Trump - in being made to fight to defend their work in the face of attacks by opponents of environmental regulation, the scientists' chances of shaping policy diminished.

"The more [government agencies] are publicly drawn into these battles, the more there will be polarisation and politicisation of them, too," Saunders said.

For example, by needlessly accusing Obama of tapping his New York headquarters, Trump has left the FBI feeling that it must defend itself against the implicit charge that it conducted itself illegally - and in pushing back against Trump, the FBI risks the appearance of playing politics which, in turn, endangers its credibility.