The Comey dismissal could become part of a widening investigation into whether the President tried to interfere with the ongoing Russian Federation probe.
Earlier this week, The Washington Post reported Mueller was investigating the possibility the President obstructed justice by suggesting then-FBI Director James Comey drop an FBI investigation into Michael Flynn. The investigation, headed by special counsel Robert Mueller, is examining whether the Trump campaign colluded with the Kremlin to help get Trump elected.
The latest White House crisis struck on the evening of Trump's 71st birthday, after a day in which he had won plaudits for his handling of the shooting of Republican Congressman Steve Scalise.
Mueller is investigating Russian interference in US elections and possible Russian ties to the Trump campaign. "Witch Hunt", Trump tweeted on Friday morning.
Trump also trained his fire on his onetime rival Hillary Clinton.
Trump said that "nobody has been able to show any proof yet"."After 7 months of investigations & committee hearings about my "collusion with the Russians", nobody has been able to show any proof".
Ryan is a former general counsel for the Senate's committee on governmental affairs.
In an address to the country, Trump struck a notably less partisan tone in response to his first major domestic crisis.
She said Trump has "embarked on an effort to undermine anyone with the ability to bring any misdeeds to light" and the Senate shouldn't let that happen.
This widening Russian Federation probe has also prompted close Trump associates to start "lawyering up".
Mueller is also looking at a second line of inquiry: whether, if any potential offenses were committed, Trump or others attempted to cover them up or obstruct the investigation into them, the source said.
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Vice President Mike Pence has also hired a private lawyer to represent his interests in the expanding probe.
Trump, who on Friday confirmed he's being investigated by the Special Counsel, has dismissed the Russian Federation investigation as a "witch hunt".
Special Counsel Robert Mueller likely "will be archiving these various Twitter rants as supplemental evidence" for the obstruction investigation, Moss, who also is deputy executive director of the James Madison Project, told VOA.
Trump may be referring to Deputy Attorney General Rod Rosenstein, who in a memo to Trump raised concerns over Comey's performance.
Mr Mueller was appointed special counsel to investigate Russian involvement in the 2016 presidential election and possible collusion by Mr Trump campaign associates with the Russians, but there has been no indication that Mr Mueller told Mr Trump to fire Mr Comey. Though just over half of Americans say they disapprove of Trump's firing of Comey, the number grows to 79 percent among Democrats. President Trump has vigorously objected to the propriety of such an investigation.
USA employers pulled back on hiring in May by adding only 138,000 jobs, though the gains were enough to help nudge the unemployment rate down to a 16 year-low.
President Donald Trump is touting his social media following, saying he can deliver his message directly to voters instead of going through the "fake news media". When asked about it Friday, the vice president dismissed it as "routine". If they find none, I'm certain Mueller will forthrightly report that fact - but only after completing a proper investigation, which takes time.
After all, how many people would know something like this? Overall, only 22 percent of Americans support Comey's dismissal.
President Trump now finds himself exactly where he doesn't want to be: under investigation by a dogged, highly respected prosecutor who owes him no personal or political loyalty.
Trump's Twitter response followed days of intensifying criticism of Mueller from some conservatives, who have charged the former Federal Bureau of Investigation director and his team with political bias and have claimed his relationship to Comey and an earlier meeting with Trump amount to conflicts of interest.
Several top intelligence officials have agreed to be interviewed by Mueller's team, according to reports in both The Washington Post and New York Times.