WASHINGTON
President Donald Trump on Thursday derided the appointment of a special counsel to lead an ongoing probe into potential collusion between his presidential campaign and Russia in last year's election.
"This is the single greatest witch hunt of a politician in American history!," Trump wrote on Twitter just hours after the Justice Department announced former FBI Director Robert Mueller would lead the bureau's ongoing probe.
The decision comes amid mounting concerns about Trump's potential attempts to interfere in the investigation, including the sacking of former FBI Director James Comey last week.
Multiple news outlets reported Tuesday that prior to ousting Comey, Trump asked him to terminate an investigation into former National Security Advisor Michael Flynn.
The retired general who has been the focus of attention after Trump fired him amid scandal, will not comply with a Senate panel's subpoena to provide documents of his interactions with Russian officials.
"General Flynn's lawyers said he would not honor the subpoena, and that's not a surprise to the committee, but we'll figure out on Gen. Flynn what the next step, if any, is," said Senate Intelligence Committee Chairman Richard Burr.
The committee's investigation, which is separate from the FBI's, will continue nonetheless, Burr said.
Flynn's lawyers had earlier requested immunity in exchange for his testimony -- an offer rejected by lawmakers.
In announcing the appointment of a special counselor on Wednesday, Deputy Attorney General Rod Rosenstein said he determined the move was "in the public interest".
But Rosenstein's decision prompted further outrage from Trump.
"With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special counsel appointed!," Trump wrote.
At a news conference with his Colombian counterpart, Trump appeared to walk back his criticism, saying he respects Mueller's appointment, but added it ultimately divides the country.
He alsp repeated his denial of any personal or campaign collusion with Russia.
"There is no collusion between certainly myself and my campaign, but I can always speak for myself, and the Russians – zero," he said.
Mueller served as FBI director under Democratic and Republican administrations from 2001 - 2013, and is highly respected in Washington.
He served beyond the normal 10-year term for directors in order to allow time for Comey to be confirmed.
He will resign his post at a private law firm in order to avoid potential conflicts of interest, the Justice Department said.
