WASHINGTON (AP) — President Donald Trump directed the U.S. intelligence community on Thursday to “quickly and fully cooperate” with Attorney General William Barr’s investigation of the origins of the multi-year probe of whether his 2016 campaign colluded with Russia.

The move marked an escalation in Trump’s efforts to “investigate the investigators,” as he continues to try to undermine the findings of special counsel Robert Mueller’s probe amid mounting Democratic calls to bring impeachment proceedings against Trump.

Press secretary Sarah Sanders said in a statement that Trump is delegating to Barr the “full and complete authority” to declassify documents relating to the probe, which would ease his efforts to review the sensitive intelligence underpinnings of the investigation. Such a move could create fresh tensions within the FBI and other intelligence agencies, which have historically resisted such demands.

Barr has already asked John Durham, the U.S. attorney in Connecticut, to examine the origins of the Russia investigation to determine whether intelligence and surveillance methods used during the probe were lawful and appropriate. Still, Barr has been directly involved, according to a person familiar with the matter who was not authorized to discuss it publicly, and is also working with CIA Director Gina Haspel, Director of National Intelligence Dan Coats and FBI Director Christopher Wray.

Trump has frequently claimed his campaign was the victim of “spying,” though the intelligence community has insisted it acted lawfully in following leads in the Russia investigation and conducted surveillance under court order.

Wray vocally opposed the release by Congress last year of details from a secret surveillance warrant obtained by the bureau on a former campaign adviser, Carter Page. The White House had eagerly encouraged Republicans on the House intelligence committee to disclose that classified information, believing it could help undermine the Russia investigation.