WASHINGTON (AFP) - Democrats erupted in outrage on Friday (June 11) over news that Donald Trump's Justice Department secretly surveilled lawmakers probing possible collusion with Russia, reaping the phone records of top political foes in what they called an unprecedented abuse of power.

Democrats Adam Schiff and Eric Swalwell said they were recently told by Apple that during 2017-2021 the company had been ordered to hand over records of their phone communications, as well as those of family members including a child, as Trump fought a flow of damaging leaks on his 2016 election campaign's links to Russia.

No proof of them being behind the leaks was ever found, yet the probe was kept alive for as long as Trump remained in office, to January 2021.

Schiff called it "the weaponisation of law enforcement by a corrupt president."

"The politicisation of the department and the attacks on the rule of law are among the most dangerous assaults on our democracy carried out by the former president," he said in a statement.

Senate leaders threatened to subpoena two Trump attorneys-general, Jeff Sessions and Bill Barr, who oversaw the surveillance, to testify on the issue.

"This is a gross abuse of power and an assault on the separation of powers," said Majority Leader Chuck Schumer and Senate Judiciary Committee Chair Dick Durbin.

The Justice Department, now led by Attorney-General Merrick Garland, appointed by Democratic President Joe Biden, said on Friday that its inspector-general would investigate the use of subpoenas and other powers to probe lawmakers and journalists under Trump.

Echoes of Watergate

Analysts called the collection of lawmakers' phone data one of the most egregious abuses by a president since Richard Nixon's early 1970s Watergate scandal.

The secret surveillance took place as Trump faced investigations by special counsel Robert Mueller and by the House Intelligence Committee - where Schiff was then the top Democrat - into whether his campaign colluded with Russian election meddling and whether Trump tried to obstruct those investigations.

As those investigations progressed and the threat of impeachment intensified, Trump accused Schiff and other Democrats of leaking classified intelligence to reporters.

It was not known if Trump explicitly told the Justice Department to investigate Schiff and Swalwell.

But between 2017 and 2020 he repeatedly accused Schiff of leaks, tweeting some 350 times about the senior Democrat, who became chairman of the Intelligence Committee in 2019 and led Trump's first impeachment trial in January 2020 - which ultimately saw the president acquitted by the Republican-led Senate.

Swalwell said the investigation appeared to begin in 2017, with the Justice Department telling Apple to hand over metadata records of calls and texts - essentially the phone numbers of those in contact with the subjects of the probe - though not the content of those communications.

The surveillance remained secret because Apple was placed under a "gag order" that was renewed three times between 2017 and 2020, even though no charges were generated.

Swalwell and Schiff only learned of the surveillance in May after the last gag order on Apple expired.

'Fishing expedition'

Collecting a lawmaker's phone records is virtually unheard of, except in corruption investigations. And even then the Justice Department handles the cases gingerly.

Surveilling members of Congress - particularly rivals of the president's Republican party - is an extreme case that would demand strong justification and top-level approval in the department.

With some 100 people covered, it appeared a poorly justified "fishing expedition," Schiff said.

But the revelation came on the back of Justice Department admissions that under Trump it collected the phone records of a number of high-profile journalists in leak investigations.

The surveillance came, Swalwell said, because the House Intelligence investigation turned up information "that the president didn't like. We showed that the president sought help from Russia, benefitted from help from Russia" in the 2016 election.

"This is about everyday Americans who don't want government to weaponise law enforcement against them because of their political beliefs," he said.