Barr Got More Power to Review the Russia Inquiry. Here’s What We Know About Its Origins.

WASHINGTON — President Trump has given Attorney General William P. Barr extraordinary powers to declassify intelligence secrets as part of his review into how the 2016 Trump campaign’s ties to Russia were investigated. That means Mr. Barr could make documents or information from the C.I.A. or the F.B.I. public over their intense objections, setting up a possible confrontation between the law enforcement and intelligence communities.

As the president tries to find evidence that he was the target of a political witch hunt, former and current intelligence officials are worried about the exposure of secret sources and sensitive methods. “This was an attempted takedown of the president of the United States,” Mr. Trump said on Friday.

Here is what we know about the origins of the investigation.

In July 2016, WikiLeaks released Democratic emails stolen by Russian military intelligence officers and posted thousands of internal Democratic National Committee documents revealing information about the Clinton campaign. That same month, the F.B.I. learned that a Trump campaign adviser, George Papadopoulos, had told an Australian diplomat that he was told that the Russians had stolen Democratic emails before they were made public. F.B.I. agents traveled to London to interview the diplomat and his assistant.

Those interviews, along with information about Russian hacking, were used to open the F.B.I.’s investigation into whether any Trump associate had conspired with the Russian government. On Friday, Mr. Trump said he hoped that Mr. Barr would scrutinize the roles of the Australian and British governments in the opening of the F.B.I.’s Russia investigation. Both countries work closely with the F.B.I. and the C.I.A.

The F.B.I. focused on the men because of their Russian contacts. Mr. Flynn and Mr. Papadopoulos later pleaded guilty to lying to the F.B.I. as part of the inquiry. Mr. Manafort was also convicted of tax fraud and other charges brought by the special counsel, Robert S. Mueller III, who took over the investigation in May 2017, and pleaded guilty to conspiracy.

Mr. Mueller’s investigators concluded that they did not have enough evidence to make a case that the men conspired with Russia’s election interference campaign. Investigators “did not find evidence likely to prove beyond a reasonable doubt that campaign officials such as Paul Manafort, George Papadopoulos and Carter Page acted as agents of the Russian government — or at its direction, control or request — during the relevant time period,” they wrote.

Mr. Trump and his allies have focused their attention on the F.B.I.’s use of an informant who met with Mr. Page and Mr. Papadopoulos to better understand the extent of their possible contacts with Russians. The informant, Stefan Halper, an American academic who taught at Cambridge University in Britain, met with the men while they were still Trump campaign advisers. Mr. Page visited Mr. Halper’s house in Virginia in August 2016, and Mr. Halper arranged a meeting with Mr. Papadopoulos the next month in London.

The F.B.I. director, Christopher A. Wray, has said he was unaware of any illegal surveillance and has refused to call agents’ work “spying.”

In October 2016, more than two months after the investigation was opened, F.B.I. agents and federal prosecutors obtained approval from a federal judge to wiretap Mr. Page. Mr. Trump’s allies have pointed to the warrant as major evidence that law enforcement officials were abusing their authority.

The wiretap application partly relied on Democratic-funded opposition research compiled into a dossier by Christopher Steele, a former British intelligence officer who was also an F.B.I. informant. Former officials have long maintained that the dossier was not used to open the investigation in July 2016.

Because the story involves an attack on an American election by a foreign adversary, presidential authority, the national security bureaucracy and other levers of power, and because Mr. Trump persists in accusing the government officials who investigated him and his campaign of an illegal witch hunt — or as he said on Friday, the “greatest hoax probably in the history our country.”

No longer constrained by the Mueller investigation, Mr. Trump appears determined to find ways to prove his accusations that the American intelligence community acted inappropriately.

Mr. Trump’s allies and other skeptics have also suggested that the Russia investigation actually began earlier than F.B.I. officials have said, suggesting that the bureau and foreign partners were plotting to take down Mr. Trump, rather than opening an inquiry based on facts. The Australian diplomat meeting with Mr. Papadopoulos was “paper cover for an investigation of the Trump campaign that was already underway,” Andrew C. McCarthy, a former federal prosecutor and contributing editor, wrote in National Review, a conservative magazine.

In his report, Mr. Mueller reaffirmed that the F.B.I. had opened the Russia investigation after receiving the information about Mr. Papadopoulos from the Australian government on July 26, 2016.

The attorney general has echoed the president’s concerns about spying on Mr. Trump’s campaign. Mr. Barr recently assigned John H. Durham, the top federal prosecutor in Connecticut, to examine the origins of the Russia investigation in a review that the attorney general is overseeing.

Mr. Barr also wants to know what the C.I.A. and other American intelligence agencies were doing in 2016 and what they knew about Russia’s effort to sabotage the election. The C.I.A. director, Gina Haspel, was the agency’s station chief in London in 2016 when Australian officials passed Mr. Papadopoulos’s information about Russia’s email hacking to the United States and when Mr. Halper arranged his meeting with Mr. Papadopoulos. It is not clear what Ms. Haspel knew about the operation, but a person familiar with the events said that the British intelligence service MI-5 was made aware of F.B.I. activities in London.

On Friday, the president said he hoped that Mr. Barr would look at Britain: “We’re going to find out what happened and why it happened.”