President Donald Trump. Credit:Bloomberg Yates and former CIA director John Brennan were to appear before the committee on Tuesday - a hearing that Nunes unilaterally cancelled after it became known that Yates and Brennan were likely to challenge White House assertions on events that led to the sacking of Trump national security adviser Mike Flynn, after he was revealed to have lied about the substance of his communications with Russian ambassador Sergey Kislyak. Democrats on the committee suspect that, in cancelling the scheduled hearing, Nunes acted at the behest of the White House - to head off the embarrassing implications of invoking executive privilege. "[Yates] sought permission to testify from the White House. Whether the White House's desire … to keep her from providing the full truth on what happened contributed to the decision to cancel today's hearing, we do not know," said Adam Schiff who serves as the intelligence committee's ranking Democrat. "We would urge that the open hearing be rescheduled without delay and that Ms Yates be permitted to testify freely and openly." Yates played a pivotal role in Flynn's demise. As acting attorney-general, it fell to her in January to advise the White House that routine surveillance of the ambassador's communications had revealed that Flynn had been lying - and thereby had left himself open to blackmail by Moscow.

Devin Nunes. Credit:AP Referring to evidence Yates might give on her conversations with White House Counsel Donald McGahn, a March 24 Justice Department letter informs Yates' lawyer David O'Neil that she needed to seek a clearance from the White House because "such communications are likely covered by the presidential communications privileges and possibly the deliberative process privileges … The president owns those privileges." Describing that argument as "overboard, incorrect and inconsistent" with past protocols on officials appearing before committee investigations, O'Neil writes: "Requiring Ms Yates to refuse to provide such information is particularly untenable given that multiple senior administration officials have publicly described the same events." Sally Yates brought details of Flynn's calls with Russia to the attention of the President. Credit:AP Schiff said that Yates was to give evidence on Flynn's phone calls to the ambassador and "about the events leading up to [Flynn's] firing, including his attempts to cover up his secret conversations with the Russian ambassador".

Asked about the Justice Department letters, presidential spokesman Sean Spicer said the White House would not bar Yates from testifying. Russian Ambassador Sergey Kislyak Credit:AP "I hope she testifies; I look forward to it." Spicer also rejected the Democrat charges that Nunes had cancelled the Tuesday hearing in response to pressure from the White House. Democrat Representative Adam Schiff said that Yates was to give evidence on Flynn's phone calls to the ambassador. Credit:AP

After a wild week as chairman of the committee, Nunes is besieged by Democrats demanding that he recuse himself or that he be sacked - and even some among his Republican colleagues are critical of his conduct. But on Tuesday, Nunes said he was going nowhere and House Speaker Paul Ryan backed him. House Speaker Paul Ryan has backed Devin Nunes. Credit:AP The calls follow revelations of a mysterious, late-night adventure, in which Nunes abandoned his staff in downtown Washington, jumping from one car to another, to attend a meeting in the White House complex with a source who shared secret intelligence reports. Nunes claimed later the reports showed that US surveillance of foreigners might have "incidentally" eavesdropped on Trump or some in his inner circle.

Trump then claimed Nunes' assertion "somewhat vindicated" his stunning tweet on March 4 that Obama had ordered wiretaps on Trump Tower. Nunes refused to shed any light on who had allowed him to view what he described as "dozens" of intelligence reports at the White House. But Schiff and other senior Democrats are arguing that his close relationship with Trump and the White House makes the committee chairman's position untenable - and speculating that he has been acting on instructions from the White House. "The public cannot have the necessary confidence that matters involving the President's campaign or transition team can be objectively investigated or overseen by the chairman," Schiff said on Monday night. Nunes seemingly is digging a hole for himself by claiming, through a spokesman, that he had to go to the White House because he needed access to a secure location to view classified material - but as one of just eight congressmen who get to hear all the national secrets, he has his own secure facility, the Capitol.

And the air of mystery deepened on Monday when presidential spokesman Sean Spicer claimed that White House officials were unaware of the Nunes visit - and at the same time, that they were "not concerned" that someone in the executive branch might have leaked classified information to Nunes. The committee chairman further angered committee Democrats by seeking a meeting with Trump to share an account of the intelligence reports before he had informed them. Defending his actions in a Fox News interview, Nunes said he "had a duty and obligation" to inform Trump about the possible surveillance "because as you know, he's taking a lot of heat in the news media". Nunes, who served on the Trump transition team, is so closely allied with the White House that some in the intelligence community are reticent about giving him further access to classified information, according to a report in The New York Times. Most peculiar in all of this is the fact that, along with FBI director James Comey, Nunes has dismissed Trump's claim that the former president ordered surveillance on Trump Tower - and a sense that Nunes is not even sure of the contents of the classified material he was shown at the White House. Here's an exchange from a press conference he gave last week:

Reporter 1: Was the President also part of that incidental collection of his communications? Nunes: Yes. Reporter 2: Excuse me, let me just clarify - the President of the United States' personal communications were intercepted as an incidental part of intelligence gathering? Nunes, after a pause: When we talk about intelligence products here, we've got to be very careful. There's confusion at the White House too - because it seems that Trump already had been made aware of the material that Nunes so desperately needed to brief him.

Spicer seemed genuinely at a loss, telling a Friday briefing: "I did not sit in on that briefing. I'm not - it just doesn't - so I don't know why [Nunes] would brief the House Speaker and then come down here to brief us on something that we would have briefed [Trump] on. It doesn't really seem to make a ton of sense. So I'm not aware of it, but it doesn't really pass the smell test." Observing the conduct of both sides on the House Intelligence Committee, Mike Rogers, who in his time as a GOP congressman headed the intelligence committee, issued a dire warning about where this investigation is headed. Loading "It sows distrust, it shows they don't have a good working foundation for really hard things. Everybody wants to find what they want to find to affirm their political position. That's no way to run an investigation," he told The Washington Post. In that, Rogers seems to be saying that the committee has become unworkable - is that the madness in Nunes' method?