President Trump took extraordinary steps on Thursday to give Attorney General William P. Barr sweeping new authorities to conduct a review into how the 2016 Trump campaign’s ties to Russia were investigated, significantly escalating the administration’s efforts to place those who investigated the campaign under scrutiny.

In a directive, Mr. Trump ordered the C.I.A. and the country’s 15 other intelligence agencies to cooperate with the review and granted Mr. Barr the authority to unilaterally declassify their documents. The move — which occurred just hours after the president again declared that those who led the investigation committed treason — gave Mr. Barr immense leverage over the intelligence community and enormous power over what the public learns about the roots of the Russia investigation.

The order is a change for Mr. Trump, who last year dropped a plan to release documents related to the Russia investigation amid concerns from Justice Department officials who said making them public could damage national security. At the time, the president was being encouraged by a group of Republican Congress members to declassify the information.

Mr. Barr, who has used the word “spying” to describe how the Trump campaign was investigated, has been deeply involved in the department’s review of how intelligence was collected on the campaign. Mr. Barr has told Congress that he personally authorized the review. While he has asked John H. Durham, the United States attorney in Connecticut, to spearhead it, a Justice Department official said that Mr. Barr has personally met with the heads of the intelligence agencies to discuss the review and that the project was a top priority after the release last month of the special counsel’s report.