Donald Trump's own party has warned the President against ousting the man leading the investigation into whether Russia interfered in the United States election.
Trump launched a Twitter tirade against Special Counsel Robert Mueller, saying his team of investigators are full of hardened Democrats who were biased against him.
The President also took aim at former FBI Director James Comey and his former deputy Andrew McCabe who said their notes from conversations with him are "fake memos".
Mueller's investigation is looking at whether Russia interfered in the 2016 election and if there are any links to the Trump campaign.
It is also looking at whether Trump sought to obstruct justice.
Members of the Republican party have urged the President not to cross a red line, saying targeting Mueller could spell the "beginning of the end" for him.
Republican heavyweight Senator Lindsey Graham told CNN it was vital Mueller was allowed to get on with the job at hand.
"He is following the evidence where it takes him and I think it's very important he be allowed to do his job, without interference," he said.
"And there are many Republicans who share my view."
Senator Graham also told the broadcaster that any move to oust the Special Counsel, "would be the beginning of the end of his presidency". "Because we're a rule-of-law nation," he said.
The President has long been torn over how to approach the Mueller probe.
Trump insists his campaign did not collude with Russia, and his legal team, namely lawyer Ty Cobb, has counselled the President to co-operate with Mueller.
However, some former campaign advisers have urged Trump to be combative, warning him that the investigation poses an existential threat to his presidency.
Trump's attacks raised new concerns among members of Congress that he could be seeking to orchestrate Mueller's firing.
Both sides of politics have warned Trump to not even think about it.
Democrat Senator Dick Durbin called for the passage of bipartisan bills designed to protect Mueller that have stalled in Congress.
"This President is engaged in desperate and reckless conduct to intimidate law enforcement agencies of this country and to try and stop the special counsel. That is unacceptable in a democracy," Durbin said.
Trump cannot directly fire Mueller.
Representative Adam Schiff, the top Democrat on the House Intelligence Committee, told ABC that firing Mueller "would undoubtedly result in a constitutional crisis".
In a morning flurry on Twitter, Trump insisted that Mueller's team of investigators is staffed with "hardened" Democrats biased against him.
"Does anyone think this is fair? And yet, there is NO COLLUSION!" Trump wrote. The night before, he had tweeted, "The Mueller probe should never have been started."
The outburst was the latest in a growing confrontation over Mueller's investigation,
Trump also took aim at former FBI deputy director Andrew McCabe, who was sacked on Friday two days before his retirement, and Comey, whom Trump fired last year over the Russia probe.
McCabe had an early role in the Russia inquiry and has knowledge of Trump and Comey's interactions.
In earlier tweets, Trump accused Comey of lying under oath in congressional testimony and dismissed as "fake memos" contemporaneous notes McCabe and Comey took of their interactions with the President.
Those memos could be fodder for Mueller's probe regarding potential obstruction of justice by the US leader.
Tweet fact check
In an analysis for the Washington Post, Glenn Kessler points out a series of inaccuracies in Trump's Twitter storm.
Kessler analysed Trump's tweets on March 17 and 18 and found the President wasn't quite accurate with his claims.
In one post, Trump said the House Intelligence Committee concluded there was no collusion between Russia and the Trump campaign.
However, as Kessler points out, the "Republican majority offered a preliminary set of conclusions, released in a one-page summary of a draft 150-page report, which said they found no evidence of collusion, co-ordination, or conspiracy."
In another tweet, Trump asks why the Mueller team has 13 Democrats and zero Republicans.
According to Kessler, this was also incorrect since Mueller was a registered Republican as is the man who appointed him, Rod Rosenstein.
It is correct that 13 of the 17 members of the investigation were registered Democrats and nine donated to the party.
However, most of the $57,000 came from one person who also donated to the Republicans.
Kessler points out Trump also donated to the Democrats, including seven times for Hillary Clinton before he decided to run for President.
The President was also a registered Democrat from 2001 until 2009.
- With AP