President Donald Trump said Friday that government officials and others who conspired to conduct surveillance on his 2016 campaign should be subject to long prison terms for committing treason.

'My Campaign for President was conclusively spied on,' he wrote in an early morning tweet. 'Nothing like this has ever happened in American Politics.'

'A really bad situation. TREASON means long jail sentences, and this was TREASON!'

The president didn't name anyone he thinks committed treason. But he has previously applied that word, and other similar brands like 'traitor,' to numerous former senior officials.

Former FBI Director James Comey, former Director of National Intelligence James Clapper, former FBI Deputy Director Andrew McCabe and others have roused his ire.

In another tweet on Friday, Trump quoted an unspecified person on the morning's 'Fox & Friends' broadcast explaining the likely fallout from Special Counsel Robert Mueller's decision not to claim the president committed a crime.

'What happened is that Donald Trump won. Down goes Comey,' the quote read.

President Trump said Friday that people who spied on his campaign committed treason and must be held accountable

Treason 'means long jail sentences,' the president tweeted, but he didn't name any names

Attorney General WilliamBarr has appointed U.S. Attorney for the District of Connecticut John Durham to investigate whether the FBI's methods of collecting intelligence on Trump's 2016 campaign were legal

A federal law defines treason as an action that 'levies war' against the United States 'or adheres to their enemies, giving them aid and comfort within the United States or elsewhere.'

The crime is punishable by death, or by a jail sentence that's 'not less than five years.'

Barr said the presence of an infamous 'anti-Trump 'dirty dossier' among the FBI's investigative documents gave him pause.

'It’s a very unusual situation to have opposition research like that, especially one that on its face had a number of clear mistakes and a somewhat jejune analysis,' he said.

'And to use that to conduct counterintelligence against an American political campaign is a strange, would be strange development.'

'The answers I’m getting aren’t sufficient,' Barr added.

Attorney General William Barr has opened an investigation into how the Justice Department's broad Russia probe began, including the process through which the DOJ persuaded a judge in a secret federal court to grant surveillance warrants against then-Trump foreign policy adviser Carter Page.

Barr told Fox News on Thursday that his preliminary look isn't reassuring.

Durham, the new spy-hunter, has previously served as a special prosecutor investigating allegations of impropriety by intelligence officials

'I’ve been trying to get answers to the questions and I've found that a lot of the answers have been inadequate and some of the explanations I've gotten don't hang together,' Barr said. 'In a sense I have more questions today than when I first started.'

'People have to find out what the government was doing during that period,' he said. 'If we're worried about foreign influence, for the very same reason we should be worried about whether government officials abuse their power and put their thumb on the scale.'

Barr emphasized that he hadn't yet drawn any conclusions.

'I'm not saying that happened but it's something we have to look at,' he said.

Trump has long believed that Obama-era DOJ officials plotted to prevent his victory over Hillary Clinton, citing text messages from a former FBI agent and his FBI lawyer paramour.

Peter Strzok and Lisa Page famously chatted that they would 'stop' Trump's ascent. They both worked on Special Counsel Robret Mueller's expansive investigation.

Citing them and others, Trump told Fox News host Sean Hannity in March that 'they wanted to do a subversion. It was treason. It was really treason.'

'If the Republican Party had done this to the Democrats, if we had done this to President Obama, you'd have 100 people in jail right now and it would be treason. It would be considered treason and they'd be in jail for the rest of their lives.'

Trump has insisted that he didn't order Barr to take an investigative baton and run with it aggressively.

'I didn't ask him to do that,' Trump told reporters outside the White House before departing for Louisiana Tuesday morning. 'I didn't know it, but I think it's a great thing that he did it.'

'It was the greatest hoax ever perpetrated on the people of this country,' Trump said of the Russia probes. 'And you know what, I am so proud of our attorney general that he is looking into it. I think it's great. I did not know about it, no.'

Barr appointed U.S. Attorney for the District of Connecticut John Durham to investigate the origins of the Russia probe.

Durham will examine whether the FBI's methods of collecting intelligence on Trump's 2016 campaign, which ultimately led to the investigation, were legal.

Previously, Durham served as a special prosecutor investigating improper behavior by intelligence officials.

The attorney general signaled during a hearing before the Senate Judiciary Committee last month that he wanted to review the law enforcement agency's surveillance of the Trump campaign. He said 'spying did occur,' but clarified that it was not necessarily illegal spying.

Trump and Republicans assert that the FBI used 'illegal' and irregular methods to obtain the Foreign Intelligence Surveillance Act warrant, which allowed the agency to spy on Trump's campaign adviser Carter Page.

A former lawyer at the FBI admitted that the agency relied heavily on the Steele Dossier, a document authored by former British spy Christopher Steele that Russians allegedly used to blackmail Trump, to obtain a FISA warrant to spy on Page.

During the hearing, Barr said it was possible some of the elements of the dossier could be part of a disinformation campaign by Russia.

If it is found that the FBI obtained the FISA warrant to spy on Trump's campaign illegally, it would bring into question the whole origins of the Russia probe.

Barr was brought to testify before the committee in April following the release of a redacted-version of Special Counsel Robert Mueller's Russia report.

Initially, Barr issued a four-page summary of the 448-page report in late March, and later in mid-April gave Congress a version where 10 per cent was blacked out for various reasons. That version was made public.

The report found that Trump, including those within his campaign and administration, had not conspired with the Russian government to influence the 2016 election.

'They want to look at how that whole hoax got started,' Trump said of the federal prosecutor's appointment. 'It was a hoax. And even Mueller – not a friend of mine – even Bob Mueller came out, 'no collusion.''

Trump has complained about a growing list of Obama-era Justice Department officials in the past, calling many of them 'traitors' and saying the Mueller probe was 'treasonous'; pictured, clockwise from top left, are former FBI Director James Comey, his former deputy Andrew McCabe, former FBI lawyer Lisa Page and former FBI senior agent Peter Strzok

Even though the report found there was no collusion, it did outline 10 'episodes' where the president could have potentially attempted to obstruct justice throughout the investigation.

Trump claims the report fully exonerated him from all crimes related to the Russia investigation, but Democrats feel there is enough evidence to begin impeachment proceedings on grounds of obstructing an ongoing investigation.

Democrats on the House Judiciary Committee have subpoenaed Barr to produce the full, unredacted report, complete with grand jury testimony. When he refused, the committee said it would hold Barr in contempt of Congress.

Despite the subpoena, Federal Rules of Criminal Procedure prohibit the attorney general from disclosing a matter that occurred before the grand jury. If he were to reveal this information to Congress, he could be held in contempt of court.