On Friday afternoon, after a week of recriminations, soul-searching, and wild-eyed hysterics over William Barr’s four-page summary of the Mueller report, the attorney general issued a correction of sorts. “My March 24 letter was not, and did not purport to be, an exhaustive recounting of the Special Counsel’s investigation or report,” he wrote to Congress, though his letter was widely interpreted as such. Instead, Barr explained, his summary merely outlined the “principal conclusions” of the Russia probe—the “bottom line,” as it were. Robert Mueller’s full report, he revealed, is nearly 400 pages long. By “mid-April, if not sooner,” the public will learn why Mueller “did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities.”

Or maybe not. In his letter to Congress, Barr said he is working with Mueller to make a number of redactions. There is material that “by law cannot be made public”; material that would compromise sensitive intelligence sources and methods; material that could affect other ongoing investigations; and information that would “unduly infringe on the personal privacy and reputational interests of peripheral third parties.”

This, of course, is the dark heart of the Mueller probe: classified intercepts of phone calls with the then-Russian ambassador, secret meetings in London and the Seychelles, cryptic communications featuring Kremlin agents and a mysterious professor and Middle Eastern fixers worthy of a John le Carré novel. These are the connections that define the Russiagate conspiracy. Yet a full accounting of their linkages and significance may never be made public.

We know that in May 2017, just after Donald Trump fired James Comey, the F.B.I. launched a counter-intelligence probe into whether Trump was under the influence of Russia against American interests. As Andrew McCabe, who was at the time serving as the acting head of the bureau, explained last month in an interview with The Atlantic, “We were concerned, and we felt like we had credible, articulable facts to indicate that a threat to national security may exist.” Put simply, top American intelligence officials feared that the president of the United States was acting as a Russian agent.

But counter-intelligence probes, such as the one that Mueller took over when he was appointed as special counsel, are not typically focused on bringing criminal charges. “The difference between a counter-intelligence and a criminal investigation, again, is that a counter-intelligence investigation doesn’t necessarily mean that they are investigating a criminal violation of the law,” Jeffrey Ringel, a former F.B.I. special agent, told me. “What they are doing is looking into the allegation that a foreign power has somehow tried to compromise an individual to further the foreign power’s ability to gather intelligence, and the person being targeted may knowingly or unknowingly be assisting a foreign power.”

Many of the most astonishing episodes involving Trump or his associates colluding with Russian agents are in the public record. On the campaign trail, Trump called for Russian hackers to target Hillary Clinton; his son, son-in-law, and campaign manager met with a Kremlin-linked attorney at Trump Tower to secure “high-level and sensitive information” on Clinton, as part of what they were told was “Russia and its government’s support for Mr. Trump”; a campaign aide, George Papadopoulos, went abroad in hopes of securing a meeting between Trump and Vladimir Putin, while another adviser, Roger Stone, got in contact with Russian military intelligence. During the White House transition, there was a flurry of contacts between Trumpworld and Moscow, including an effort by Jared Kushner to establish a secret back channel with the Kremlin. Later, as president, Trump bragged about firing Comey to Russian officials in the Oval Office, sought out private meetings with Putin, and has sided with Russian intelligence over the assessments of his own agencies.