WASHINGTON, U.S. - The federal investigation into the alleged collusion between Russia and the U.S. President Donald Trump's election campaign took a potentially destructive turn last week - causing a minor tremor in Trump's camp.

The Justice Department appointed Special Counsel Robert Mueller, who is leading the Russia probe, managed to score a decisive victory, cracking one of the central figures in the entire investigation - Michael Cohen.

Cohen, the President's longtime former personal attorney, who was once known as Trump's fixer pleaded guilty to lying to Congress as part of the federal investigation into Russian collusion during the 2016 U.S. Presidential election.

He admitted that he lied to a congressional committeeabout the presidents real estate dealings in Moscow.

Cohen was referring to his 2017 testimony before the Senate Intelligence Committee, when he said that Trump abandoned negotiations to build a Trump tower in Moscow in February 2016 before the Iowa caucuses.

However, court papers revealed that Cohen admitted that he continued to brief Trump (identified as 'Individual 1' in court papers) and Trumps family members about the project into June 2016.

While the Cohen guilty plea offered more legal hurdles for Trump, Mueller's office unveiled another destructive obstacle for the President after accusing Trump's former campaign chairman Paul Manafort of breaking his own plea deal.

Mueller's office said that Manafort misled the FBI and the special counsel's team - claiming that the alleged violation by the man who managed Trump's election campaign for a brief, but crucial period in 2016 - puts at risk a 10-year cap on the time he would have to serve in prison.

The announcement by the Special Counsel's office came weeks after Manafort pleaded guilty to financial fraud as part of a plea deal that he hoped would spare him from a federal trial in Washington, DC.

Manafort, who is expected to be sentenced early next year, was found guilty in federal court in Virginia of similar financial crimes.

Mueller-bashing in the media

After the two explosive developments in the probe against his client, Trump's lead personal lawyer Rudy Giuliani made media appearances, adopting his usual Mueller-bashing strategy, aimed at discrediting the Special Counsel's investigation.

Speaking on a radio show, Giuliani accused Mueller of using unethical tactics to intimidate Cohen into pleading guilty of lying to Congress in the investigation.

Trump's top lawyer alleged, They obviously exerted a lot of pressure on him. Mr. Cohen, unfortunately, has a history of significant lies in the past."

He claimed that Mueller was trying to pressure the targets of his probe into "turning on the president at any cost."

Giuliani said, "They think they know the only truth that exists, even if there's a lot of doubt about it. They seem to want to [prosecute] people at any cost, including the cost of ethical behaviour or the rights of people. And because 70 to 80 percent of the mainstream media is biased, they let them get away with it."

The former New York mayor said, This isnt a search for the truth. Its a witch hunt. This is what is wrong with these special prosecutors and independent counsels. They think they are God. They seemed to want to prosecute people at any cost, including the cost of ethical behaviour and the rights of people.

Commenting on Cohen, Giuliani said, "It's no secret that he wanted to be [White House] chief of staff or he wanted to have some very high position in the government, and the president didn't think he was up to it, which I guess turns out to be absolutely correct. I have to suspect that that ultimately created some kind of bitterness, and when this pressure was applied to him I just don't think he withstood it."

Then, denying any collusion between the Trump campaign and Russia, Giuliani also alleged that Mueller was trying to force Manafort to implicate the president for collusion.

He said, They want [Paul Manafort] to give certain forms of evidence that would implicate the president in things that Mr. Manafort says are untrue. And they are pressuring him, and creating a real risk that the man might commit perjury. This kind of pressure can create the risk of tainted testimony.