Trump-Russia special counsel Robert Mueller was appointed May 17, 2017. Twenty-two months later, on March 22, 2019, Mueller sent his report to the Justice Department.

Some special counsel investigations have taken longer; it is the nature of such probes to drag on and on. But why did Mueller need nearly two years to determine whether the Trump campaign and Russia conspired or coordinated to fix the 2016 election?

He didn't, it appears. In the wake of the release of Mueller's report, there are indications that special counsel prosecutors mostly knew by the end of 2017, and certainly by a few months later, that the evidence would not establish that conspiracy or coordination — or collusion, to use the popular term — had taken place. Mueller clearly spent a lot of time on the other half of his report — trying to establish that Trump obstructed justice — but on the most explosive and consequential allegation of the Trump-Russia affair, the conspiracy allegation, the Mueller investigation was essentially over long before it officially ended.

"By early December, [Mueller] had exhausted all of the evidence and the witnesses," John Dowd, who was the president's lawyer for the first 10 months of the investigation, said in a recent podcast interview.

Dowd dealt with White House witnesses, and the president urged those White House staffers to talk to Mueller and provide him with documents early in the investigation. They did. The president's team also had joint defense agreements with others who talked to Mueller. That allowed Trump lawyers to know what witnesses were telling prosecutors.

By the end of 2017, Dowd and others thought that Mueller had gotten everything he could get on the question of conspiracy and coordination. "We told [the special counsel's office] in various ways that they had everything," Dowd said in a phone conversation Wednesday. "We knew what the witnesses were saying, and they knew that we knew. They knew we debriefed people."

Of course, Dowd and the Trump legal team didn't know about everybody. For example, a key figure in the conspiracy allegation, Carter Page, was not on the White House radar screen. But in a new podcast interview, Page, too, said the special counsel's office was finished with him by the end of 2017.

Page did five interviews with the FBI in March 2017, before Mueller was appointed. Page said he had just one appearance with Mueller's prosecutors, and that was in the grand jury on Nov. 17, 2017. Asked if that was the last he heard from the special counsel's office, Page said, "Yeah, essentially."

Page didn't enjoy his time with the Mueller team. "Basically it's like Guantanamo Bay detention camp in a lot of ways," Page said, "but I actually would have enjoyed being in Gitmo more than what I went through with these people."

Page was never charged with any wrongdoing.

The Mueller report cites Page's FBI interviews, while it keeps his grand jury testimony a secret. It also cites interviews of people who had knowledge of Page's July 2017 trip to Moscow and people who had knowledge of his dealings with the Trump campaign around the same time. One can look at the timing of those interviews to see when the investigation of Page was most intense.

One of the officials at the Moscow school at which Page gave a speech was interviewed by Mueller on July 28, 2017. Another such official talked on June 9, 2017. Sam Clovis, a Trump campaign official who Page told about the trip, was interviewed on Oct. 3, 2017. Corey Lewandowski, then the campaign manager who had some dealings with Page, talked on June 19, 2017.

It appears Mueller mostly, if not completely, closed the book on investigating Page by the end of 2017.

Page, of course, was not the only figure alleged to be involved in a Trump-Russia conspiracy. There was also George Papadopoulos, who was interviewed by the FBI in August and September of 2017 before pleading guilty on Oct. 5, 2017, to making false statements. (The plea was made public on October 30, 2017.) Taking a look at Mueller's Papadopoulos-related interviews, it appears the special counsel questioned all the members of Trump's foreign policy team who took part in a much-discussed March 31, 2016 meeting; those interviews took place in the fall of 2017. The Clovis interview, again on Oct. 3, 2017, was also important for the Papadopoulos matter.

Mueller never talked to the mysterious Joseph Mifsud, the Maltese professor who may have had ties to Russia and/or U.S. intelligence and who tried to feed Papadopoulos information on supposed Russian activities. And while the Mueller report mentions a "representative of a foreign government" — presumably members of the Australian diplomatic and intelligence services, who showed a deep interest in Papadopoulos — there is no indication of a Mueller interview. In any event, it appears that Mueller had what he needed on Papadopoulos by the end of 2017.

Another incident included in the conspiracy volume of Mueller's report is the accusation that the Trump campaign weakened the Republican platform to please Russia. Again, Mueller appears to have finished his investigation early. His prosecutors interviewed the Trump campaign's director of national security, J.D. Gordon, on Aug. 29, 2017. They interviewed Rachel Hoff, a GOP official who played a role in the matter, on May 26, 2017, which was during Mueller's first ten days in office. They interviewed GOP delegate Diana Denman on June 7, 2017, and another GOP staffer, Matt Miller, on Oct. 25, 2017. By then, Mueller had enough to know the platform allegation was entirely unfounded.

Finally, there was what became, in Trump accusers' minds, Exhibit A of collusion: the Trump Tower meeting. By the end of 2017, Mueller had the testimony of most of the participants. He interviewed the translator, Anatoli Samochornov, on July 13, 2017, and participants Rinat Akhmetshin and Irakly Kaveladze on Nov. 14, 2017, and Nov. 16, 2017, respectively. Mueller did not interview Donald Trump Jr. — the report noted that the younger Trump "declined to be voluntarily interviewed" by prosecutors. But Mueller had testimony from Trump Jr. before the Senate Intelligence Committee, House Intelligence Committee, and Senate Judiciary Committee. Mueller interviewed Jared Kushner on April 11, 2018. He also had extensive documentation on the meeting from all sides, including Trump Jr.

So even assuming Mueller had to wait until talking to Kushner on April 11, 2018, he had the story on conspiracy nearly a year before releasing the Mueller report.

In late 2018, the Mueller team appears to have embarked on a collusion wild goose chase, looking for evidence of a Trump-Russia conspiracy among Roger Stone and Jerome Corsi. Mueller's prosecutors interviewed Corsi over and over — on Sept. 6, 2018; Sept. 17, 2018; Sept. 21, 2018; Oct. 31, 2018; Nov. 1, 2018; and Nov. 2, 2018. Corsi was never charged with any wrongdoing.

As for Stone, on Jan. 24, 2019, Mueller indicted Stone for allegedly lying in testimony to the House Intelligence Committee on Sept. 26, 2017. Many portions of the Mueller report dealing with the Stone case are blacked out because they deal with an ongoing legal matter. But Mueller did not find collusion there, either.

Now, it is clear Mueller first looked for collusion in all the obvious places. Failing to establish that it took place, he looked farther to the fringes of the Trump-Russia affair. He failed to establish that it took place there, either. As time passed and the two-year mark for his investigation approached, he finally gave up.