Since May 2017, Mueller has been independently investigating for the US government the possible links between members of the Trump campaign and the Kremlin, which US intelligence agencies accuse of interfering in the 2016 presidential election to favour Trump. Robert Swan Mueller is an American attorney who served as the sixth Director of the Federal Bureau of Investigation from 2001 to 2013. A conservative Republican, he was appointed by President George W. Bush; President Barack Obama gave his original ten-year term a two-year extension, making him the longest-serving FBI Director since J. Edgar Hoover. He is currently head of the Special Counsel investigation of Russian interference in the 2016 United States elections and related matters. He has not made any public comment since he was named to lead the investigation into Russian interference in last year's election. Instead, he has quietly hired a team of elite Justice Department prosecutors. The last 16 months have witnessed a flurry of criminal indictments and guilty pleas, tense court appearances. Donald Trump, the US President, has been responding with angry tweets. However, it seems, Mueller already knows and what he'll investigate next.

For the allegations that the president orchestrated a campaign cover-up to buy the silence of two women who claimed he had affairs with them, Trump tweeted: "NO COLLUSION - RIGGED WITCH HUNT!" — a reference to special counsel Robert Mueller's investigation into Russian interference in the 2016 election. 

Confronting mounting legal and political threats, President Donald Trump's former lawyer and team-mate  Michael Cohen pleaded guilty in federal court Tuesday to tax evasion, bank fraud and campaign-finance violations. Cohen admitted that he had made six-figure payments to silence two women in advance of the 2016 election at Trump's direction.

Michael Cohen pleaded guilty Tuesday to total eight charges, including campaign finance violations that he said he carried out in coordination with Trump. Behind closed doors, Trump expressed worry and frustration that a man intimately familiar with his political, personal and business dealings for more than a decade had turned on him. Trump also took to Twitter to accuse his former lawyer Michael Cohen of making up "stories in order to get a 'deal'" from federal prosecutors. Cohen's lawyer Lanny Davis argued that Trump also should face legal consequences. Cohen "testified under oath that Donald Trump directed him to commit a crime by making payments to two women for the principal purpose of influencing an election."

"If those payments were a crime for Michael Cohen, then why wouldn't they be a crime for Donald Trump?" Davis asked.

However, Trump's personal lawyer, former New York mayor Rudy Giuliani, defended Trump saying the government's charges against Cohen contain "no allegation of any wrongdoing against the president."

Prez Trump's another Waterloo could be John Manafort. He is a well-known American lobbyist, political consultant, and lawyer. He had joined Donald Trump's presidential campaign team in March 2016, and was campaign chairman from June to August 2016. In August 2018, Manafort was convicted of five counts of tax fraud, two counts of bank fraud and one count of failure to report foreign bank accounts. During the presentation of closing arguments in Manafort's trial in Alexandria, Virginia, Mueller's team concluded: "When you follow the trail of Mr. Manafort's money, it's littered with lies. He is "not above the law" and added that "he lied to his tax pre-parers, he lied to his bookkeeper, because he wanted to hide that money and avoid paying taxes." Manafort had allegedly worked for foreign governments between 2006 and 2017, including pro-Russian former Ukrainian President Viktor Yanukovich, and for Russian oligarchs, whom he helped improve their images in Washington without registering those activities with the US government, an omission that constitutes a crime.

Convictions on all counts, as investigators have attempted to prove in the court documents filed to date, could result in Manafort spending the rest of his life behind bars.

Sensing the trouble, the US President Donald Trump has warned today that if he was impeached the US economy would collapse. In an interview aired today, Trump told Fox and Friends, as quoted by AFP, "I will tell you what, if I ever got impeached, I think the market would crash. I think everybody would be very poor."

They're the president's men as per circumstantial evidence and they represent two of the most worrisome prospective witnesses against Trump. They both face jail terms.

According to Harry Sandick, a former federal prosecutor with the Southern District of New York, if they decided to co-operate [with government lawyers, they could potentially have incriminating information about the president. They're both huge."