According to a memo from former FBI Director James Comey, Trump asked him to cease investigating Flynn, which many are characterizing as an obstruction of justice.
"I think it is totally ridiculous", he began.
The tweets dropped the morning after special counsel Robert Mueller picked up the Federal Bureau of Investigation probe into possible connections between Russian Federation and Trump's campaign.
The Utah Republican, who had just started his fifth term in Congress, used his post as chair of the oversight committee to doggedly investigate Hillary Clinton before the 2016 presidential election and raise his political profile.
But Mueller and Comey have been longtime allies dating back to at least 2003 when the men both worked in Washington, D.C., Mueller as FBI Director and Comey as Deputy Attorney General.
The president's comments come as he deals with backlash from firing Comey last week and subsequent reports that raised questions about whether he might have tried to interfere with an investigation.
Mr Trump on Thursday piled onto his mounting reasons for firing Mr Comey, mentioning his "very poor performance" at a recent Senate hearing, and the FBI's declining reputation.
"A lot of times he's the victim of not being a career politician", Rep. James Comer of Kentucky said of Trump. "SABOTAGE", the subject line said.
Congressional Probes While Mueller takes over the Justice Department investigation, probes in Congress were proceeding as well.
Sen. John McCain of Arizona, the chairman of the Armed Services Committee, expressed outrage Thursday at video that appears to show Erdogan's bodyguards violently breaking up a protest earlier this week outside the Turkish ambassador's residence in Washington.
FBI investigators reportedly discovered multiple contacts that are a cause for concern including Paul Manafort, former Trump Campaign Chairman, Carter Page, former Foreign Policy Advisor and Michael Flynn, the former National Security Advisor. In many cases, they represent states or districts that voted strongly for Trump, and where the GOP base still ardently supports the president.
Trump fired Flynn on February 13, on grounds that he had misled Vice President Mike Pence and other officials about his contacts with Russians.
The scope of Mueller's investigation includes "any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump".
He has become a central figure in the investigations in Congress.
Chairman Richard Burr (R-NC) speaks to the media after a Senate Select Committee on Intelligence closed door meeting at the U.S. Capitol, on May 16, 2017. The Flynn investigation was part of a broader probe into Russian interference in last year's presidential election.
He said that he thinks the appointment of a special counsel "divides the country".
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