President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE on Wednesday called on Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsRoy Moore sues Alabama over COVID-19 restrictions GOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs MORE to immediately stop the Russia investigation, a significant escalation of Trump's attacks against the long-running probe that has dogged his presidency.

The remark was Trump's most direct public appeal yet to end special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's investigation, which he has blasted for months. It also raised questions from legal experts about whether the president was attempting to obstruct justice.

In a series of morning tweets, Trump called the investigation a “terrible situation” that must be stopped “before it continues to stain our country any further.”

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“Attorney General Jeff Sessions should stop this Rigged Witch Hunt right now," Trump wrote.

The president declared that the notion his campaign conspired with Russia in its effort to interfere in the 2016 presidential election is a “TOTAL HOAX." He also made the unsubstantiated claim that Mueller, a Republican appointed by Deputy Attorney General Rod Rosenstein Rod RosensteinDOJ kept investigators from completing probe of Trump ties to Russia: report Five takeaways from final Senate Intel Russia report FBI officials hid copies of Russia probe documents fearing Trump interference: book MORE, the No. 2 Justice Department official, is "totally conflicted" and unable to carry out a fair investigation.

The tweets come at a pivotal time in the Russia probe, when Mueller is reportedly examining whether Trump's previous tweets about Sessions and former FBI Director James Comey James Brien ComeySteele Dossier sub-source was subject of FBI counterintelligence probe Judge will not dismiss McCabe's case against DOJ Democrats fear Russia interference could spoil bid to retake Senate MORE were meant to obstruct the investigation.

“Tweets like this one directing the Attorney General to stop the investigation of Trump and his friends are among the many reasons why Mueller will conclude Trump obstructed justice,” former federal prosecutor and CNN legal analyst Renato Mariotti argued in a tweet.

The White House and Trump's legal team raced to contain the fallout over the president's comments on Wednesday, saying Trump was merely venting his frustration with the special counsel probe and not giving an order to Sessions to end the investigation.

“It's an opinion. And he used a medium that he uses for opinions: Twitter. He used the word ‘should.’ He didn't use the word ‘must.’ And there was no presidential directive that followed,” Trump's personal lawyer Rudy Giuliani told reporters in New Hampshire.

That message was echoed by White House press secretary Sarah Huckabee Sanders during her briefing with reporters.

“It’s not an order, it’s the president’s opinion,” Sanders said. “The president has watched this process play out, but also wants to see this come to an end.”

Trump's comments Wednesday caused a stir on Capitol Hill, where Republican and Democratic lawmakers said the Mueller probe should be allowed to continue unimpeded.

“I think it's highly inappropriate and intemperate,” said Sen. Susan Collins Susan Margaret CollinsThe Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power Billionaire who donated to Trump in 2016 donates to Biden Credit union group to spend million on Senate, House races MORE (R-Maine), who exited an elevator to answer reporters' questions about the tweet. “It would be far better if the president just refrained from commenting and Mr. Mueller proceeds with his investigation.”

Rep. Adam Schiff Adam Bennett SchiffSchiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power Rubio on peaceful transfer of power: 'We will have a legitimate & fair election' MORE (Calif.), the top Democrat on the House Intelligence Committee and a vocal Trump critic, called the tweets "an attempt to obstruct justice hiding in plain sight."

“America must never accept it,” he tweeted.

Several Republicans expressed confidence, however, that Trump would not move to bring the investigation to a premature end.

“I think that's an academic question,” Sen. John Kennedy John Neely KennedyMORE (R-La.) said when asked if he believes Trump will fire Mueller. “I think the president is way too intelligent to fire Mueller and I don't think [Attorney] General Sessions can because he recused himself.”

Past presidents have generally refrained from weighing in on active federal investigations, but Trump has broken that norm repeatedly by denouncing the Russia probe.

Sessions has long been the target of Trump's ire over his recusal from Russia-related matters last year. Sessions's recusal left his deputy, Rosenstein, as the top Justice Department official overseeing the Russia probe, and Rosenstein appointed Mueller after Trump fired Comey.

The attorney general recused himself in March 2017 to avoid conflicts related to his service as a key Trump campaign adviser. The decision came after it was revealed Sessions failed to disclose contacts with Russia’s U.S. ambassador during the campaign.

Trump has said he would have nominated another person as attorney general if he had known Sessions would recuse himself, but previously has not gone as far as calling on Sessions to end the probe.

The Justice Department declined to comment on Wednesday.

The president's latest barrage of criticism came on the second day of the trial of his former campaign chairman, Paul Manafort Paul John ManafortOur Constitution is under attack by Attorney General William Barr Bannon trial date set in alleged border wall scam Conspicuous by their absence from the Republican Convention MORE, who is accused of committing tax, financial and bank fraud crimes while working for the pro-Russian former leader of Ukraine.

Manafort is the first Trump associate to go on trial in the Mueller probe, an event that has consumed a major amount of media coverage — to Trump's apparent frustration.

The president sought to distance himself from Manafort early Wednesday, saying in another tweet that Manafort only “worked for me for a very short time” and suggested federal authorities should have informed him his campaign chief was under investigation during the 2016 presidential race.

“Paul Manafort worked for Ronald Reagan, Bob Dole and many other highly prominent and respected political leaders. He worked for me for a very short time. Why didn’t government tell me that he was under investigation. These old charges have nothing to do with Collusion — a Hoax!” Trump tweeted.

Trump later questioned whether federal officials were treating Manafort worse than Mafia boss Al Capone, who served 11 years in prison after being convicted of tax evasion.

Capone was suspected of being involved in dozens of murders but he was never tried or convicted for them.

Looking back on history, who was treated worse, Alfonse Capone, legendary mob boss, killer and “Public Enemy Number One,” or Paul Manafort, political operative & Reagan/Dole darling, now serving solitary confinement - although convicted of nothing? Where is the Russian Collusion? — Donald J. Trump (@realDonaldTrump) August 1, 2018

For months, the president has kept up a sustained attack on the Mueller investigation in an attempt to undermine it in the eyes of the public.

He repeated those complaints during his Wednesday morning tweets, sharing quotes from attorney Alan Dershowitz, a critic of the probe, and blasting FBI agent Peter Strzok for having been “out to STOP THE ELECTION OF DONALD TRUMP.”

Strzok was removed from the Mueller probe last year after the special counsel was made aware of anti-Trump texts that the agent sent to a colleague, Lisa Page, with whom he was having an affair.

Jordain Carney and Morgan Chalfant contributed.