U.S. President Donald Trump has assailed special counsel Robert Mueller's investigation into Russia meddling in the 2016 presidential election as "a National Disgrace!"

The U.S. leader started the work week with a string of broadsides against the Mueller probe, complaining the prosecutor "is just someone looking for trouble" as he investigates Trump campaign aides' links to Russia and whether Trump, as president, obstructed justice by trying to thwart the inquiry.

Trump described Mueller as "disgraced and discredited" and said "his whole group of Angry Democrat Thugs" had interviewed White House counsel Donald McGahn for 30 hours "only with my approval, for purposes of transparency." News outlets reported that Trump and his lawyers do not know the full scope of what McGahn told Mueller's team of investigators.

Trump added, "They are enjoying ruining people's lives and REFUSE to look at the real corruption on the Democrat side - the lies, the firings, the deleted Emails and soooo much more! Mueller's Angry Dems are looking to impact the election," the nationwide November 6 congressional contests.

"Where's the Collusion?" Trump asked." They made up a phony crime called Collusion, and when there was no Collusion they say there was Obstruction (of a phony crime that never existed). If you FIGHT BACK or say anything bad about the Rigged Witch Hunt, they scream Obstruction!

FILE - Special Counsel Robert Mueller departs afte
FILE - Special Counsel Robert Mueller departs after briefing members of the U.S. Senate on his investigation into potential collusion between Russia and the Trump campaign on Capitol Hill in Washington, U.S., June 21, 2017.

Mueller's investigators have uncovered several instances of Trump campaign contacts with Russia, including a mid-2016 meeting at Trump Tower in New York in which Trump's oldest son, Donald Trump Jr., met with a woman said to be a Russian government attorney who would offer incriminating material against Trump's election challenger, Democrat Hillary Clinton. No such anti-Clinton information emerged from the meeting.

But when news of the meeting surfaced after Trump became president, he dictated a misleading statement about the talks, claiming they were about adoption of Russian children. More recently he has said it was a routine political meeting - opposition research about an election opponent - and he did not know about it in advance.

Trump also renewed his attacks on former Central Intelligence Agency Director John Brennan, after revoking Brennan's national security clearance last week. Trump called Brennan a "political hack" and "the worst CIA director in our country's history." 

Ex-CIA chief, who lost his security clearance last
Ex-CIA chief, who lost his security clearance last week, says he will do whatever he can to stop what he calls Trump's 'abuses'.

Trump said he hopes Brennan carries through on his threat to file a lawsuit to protect others from losing their security clearances because, "It will then be very easy to get all of his records, texts, emails and documents to show not only the poor job he did, but how he was involved with the Mueller Rigged Witch Hunt. He won’t sue!"

One hundred and seventy-five other former U.S. national security officers, Pentagon, and State Department officials added their names Monday to the list of those who have already come to Brennan's defense.

They include such well-known names from the Bush and Obama administrations as former deputy secretary of state Tony Blinken, former undersecretary of state Nicholas Burns, and ex-NATO commander, Adm. James Stavridis.

The officials wrote a letter stating that while they may not totally agree with Brennan's sharp criticism of Trump, they believe "strongly that former government officials have the right to express their unclassified views on what they see as critical national security issues without fear of being punished for doing so."

Trump, however, has dismissed their favorable comments about Brennan, saying, "Everybody wants to keep their Security Clearance, it’s worth great prestige and big dollars, even board seats, and that is why certain people are coming forward to protect Brennan. It certainly isn’t because of the good job he did!"

Mueller has secured guilty pleas from several Trump campaign figures, including former national security adviser Michael Flynn and foreign affairs adviser George Papadopoulos, both of whom have pleaded guilty to lying to investigators about their contacts with Russia.

Former Trump campaign adviser George Papadopoulos
FILE - Former Trump campaign adviser George Papadopoulos is seen in an undated photo (George Papadopoulos/LinkedIn)

Trump lawyer Rudy Giuliani, a former New York mayor, contended Sunday on NBC's Meet the Press that "truth isn't truth" in the Mueller investigation, saying that various events in the Trump presidency, and whether he obstructed justice by seeking to block the investigation, are open to interpretation.

Giuliani's comment was widely mocked on social media. On Monday, he sought to clarify it, saying, "My statement was not meant as a pontification on moral theology, but one referring to the situation where two people make precisely contradictory statements, the classic 'he said, she said' puzzle. Sometimes further inquiry can reveal the truth other times it doesn't."

Giuliani's statement was focused on conflicting accounts about a meeting early last year at the White House between Trump and James Comey, then director of the Federal Bureau of Investigation and leading the agency's Russia investigation before Trump fired him in May 2017.