WASHINGTON (Reuters) - U.S. Attorney General William Barr faced growing criticism from Democrats on Friday after the Justice Department said it had intensified its politically charged review of the origins of the investigation into Russian interference in the 2016 election.

A person familiar with the matter late on Thursday confirmed that the inquiry had become a criminal investigation, a sign that the federal prosecutor leading the effort, John Durham, thinks laws may have been broken.

But Democratic lawmakers and some former U.S. officials said they have seen no evidence of improper behavior, let alone illegal activity, by U.S. intelligence and law enforcement agencies during the long-running investigation, which dogged President Donald Trump for much of his presidency.

“We’ve found nothing remotely justifying this,” said Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, which has been examining the issue for three years.

Warner said Barr needs to explain himself to Congress.

Democrats and some former law enforcement officials have accused Barr, the top U.S. law enforcement official, of using the power of the Justice Department to chase unsubstantiated conspiracy theories that could benefit the Republican president politically and undermine the findings of former Special Counsel Robert Mueller’s Russia investigation.

Barr launched Durham’s investigation in May after Trump repeatedly assailed key figures involved in launching the Russia investigation. The president’s critics have said the actual purpose of the investigation is to discredit legitimate findings about Russian meddling in the 2016 election and the numerous contacts between Moscow and the Trump campaign. These critics also have accused Barr of acting as Trump’s lawyer rather than in the national interest.

Speaking to reporters at the White House, Trump said he would leave the investigation to Barr and the Justice Department.

“I think you’ll see things that nobody would have believed. This was the worst hoax in the history of our country,” Trump said.

FILE PHOTO: U.S. Attorney General William Barr participates in a presentation ceremony of the Medal of Valor and heroic commendations to civilians and police officers who responded to mass shootings in Dayton, Ohio and El Paso, Texas during a ceremony in the East Room of the White House in Washington, U.S. September 9, 2019. REUTERS/Erin Scott/File Photo

The designation that it has become a criminal investigation gives Durham, the top federal prosecutor in Connecticut, authority to convene a grand jury to assess evidence and compel testimony from witnesses - a process commonly used before criminal charges are filed in the U.S. legal system.

The person who spoke with Reuters on Thursday declined to say whether a grand jury had been set up.

“It doesn’t mean that it will end in an indictment. It just means there is enough to take it to the next level,” said Channing Phillips, who served as the top federal prosecutor in the District of Columbia under Trump’s Democratic predecessor Barack Obama.

STEELE WILL NOT COOPERATE

Durham might have trouble getting the cooperation of one figure who played a central role in the initial 2016 probe, former British intelligence officer Christopher Steele.

Steele, who assembled research used by the FBI in their investigation about connections between the 2016 Trump campaign and Russian officials, has cooperated with a separate review by the Justice Department’s internal watchdog.

Steele does not plan to cooperate with Durham’s probe, according to a source familiar with the matter, and any efforts to force him to testify could take years because he is outside the United States.

The FBI has said its employees are cooperating with the probe. Other likely targets who are now no longer in government service, such as former CIA Director John Brennan and former FBI agent Peter Strzok, previously told Reuters through representatives or attorneys they had not been contacted.

The FBI’s former No. 2 official, Andrew McCabe, said investigators did not act improperly.

“You had a room full of career government officials with a very serious responsibility of investigating threats to national security, and that’s exactly what we did,” McCabe said on CNN.

McCabe is one of several former U.S. officials who have come under scrutiny. He was fired by the Trump administration in 2018, hours before he was due to retire, after the Justice Department’s internal watchdog found he had misled investigators about his actions in 2016. McCabe’s lawyer has called it an honest mistake.

Top Justice Department officials approved a criminal case against him in August, but charges have not been filed.

Trump has alleged that U.S. officials hostile to him launched the 2016 investigation, which was eventually taken over by Mueller after the president fired FBI Director James Comey in 2017, to undermine his chances of winning the White House, although he and his supporters have provided no evidence.

Mueller’s investigation, which found that Moscow engaged in a campaign of hacking and propaganda to boost Trump’s 2016 candidacy, led to the criminal convictions of several former campaign aides. But Mueller concluded that he did not have sufficient evidence to establish a criminal conspiracy between the Trump campaign and Russia.

The Democratic chairmen of the House Judiciary and Intelligence Committees expressed concern that Barr has turned the Justice Department into “a vehicle for President Trump’s political revenge.”

“If the Department of Justice may be used as a tool of political retribution or to help the President with a political narrative for the next election, the rule of law will suffer new and irreparable damage,” Representatives Jerrold Nadler and Adam Schiff said in a statement late on Thursday.

Several lawyers who know Durham personally have said he would not be persuaded to pursue politically driven criminal charges.