WASHINGTON — By the time Robert Mueller was sworn in as special counsel in May 2017, the FBI had already opened an investigation into whether the president of the United States was under Russia's sway — and whether the president, by firing the FBI director, had sought to obstruct that inquiry.

The Mueller report, released in April, didn't definitively answer either of those questions.

And on Wednesday, Mueller himself made clear that he wasn't going to answer them either.

Reading from a prepared text, speaking for the first time after two years in the shadows, Mueller said he had no intention of testifying publicly before Congress. Even if compelled to, he said he would not go beyond the careful language of his report, which didn't deal at all with the question of Russian influence on the White House, and which pointedly declined to conclude whether the president had obstructed justice.

"The report is my testimony," said the 74-year-old Vietnam combat veteran who led the FBI after the 9/11 attacks.

It was, to some, a deeply unsatisfying end to an investigation they thought would get to the bottom of the most important questions about Donald Trump and Russia.

"Mueller had one job: To settle the most inflammatory and speculative Trump-Russia allegations once and for all," tweeted Mattathias Schwartz, who writes about national security in the New Yorker and elsewhere. "Instead, he punted… Now we're permanently stuck with two realities coexisting in one country."

Mueller didn’t punt on everything. His report very clearly says he didn’t find sufficient evidence to charge a conspiracy between the Trump campaign and Russia.

But as to the FBI’s counterintelligence investigation into whether Trump was in any way compromised by Russia over business connections, dark secrets or anything else — the report is entirely silent. And Mueller said that since he couldn't bring a charge against a sitting president, he couldn’t make a prosecutorial judgment on obstruction, either.

The two vastly different interpretations of that outcome were on stark display in the wake of Mueller's statement. The White House, most elected Republicans and their allies in the right-wing media proclaimed the special counsel's comments further evidence that he had no case against Trump. Many Democrats and Trump critics saw Mueller's remarks as a veiled signal to Congress that it must begin impeachment proceedings. Politically, it wasn't clear that anything had changed.

Mueller's backers say he did exactly what he was hired to do, within the narrow confines of the special counsel regulations: investigate how the Russians attacked the 2016 election, figure out whether any Americans helped them, and charge any crimes he found along the way.

Mueller was not operating under the independent counsel law that expired in 1999, which allowed Kenneth Starr to examine and report on conduct by President Bill Clinton that wasn't clearly criminal.

That part was known. But Mueller revealed in his remarks something few people understood about his approach: He and his team concluded early on that they could not accuse the president of a crime even informally, without charging him. They read that to mean they could not even make a decision about whether Trump obstructed justice.

"It would be unfair to potentially accuse somebody of a crime when there can be no court resolution of an actual charge," Mueller said.

That language is not part of the Justice Department doctrine that says a sitting president can't be indicted. Mueller and his team took that policy one step further, in the interest of fairness. Some would argue that an impeachment trial in the Senate would offer the president a forum to defend himself, not to mention his Twitter feed.

Mueller's fairness doctrine raises this question: What would Mueller have done had he unearthed evidence that Trump conspired with Russia over election interference? How would he have communicated that criminality to the Justice Department, Congress and the public, given that he didn't think he could accuse Trump of crimes? He didn't have to grapple with that conundrum, because his investigation found insufficient evidence to establish such a conspiracy.

But on the question of the Trump campaign's dealings with Russia, that narrow finding was the only conclusion Mueller reached, despite laying out a mountain of evidence of suspicious contacts, back channels, business deals and approaches.

Did any of those contacts with Russians compromise national security? Did the Trump team report any of it to the FBI? Did the president have any business dealings with Russians beyond the proposal to build a tower in Moscow?

Mueller's report answers none of those questions, and Mueller made clear that he never will.

At least three Congressional committees are now trying to answer them. But Congress can't charge witnesses with crimes and seek to flip them. Congress can't serve search warrants on people who might destroy evidence. Congress is bumping up against executive privilege claims by some key witnesses who spoke to Mueller's team.

On the question of potential crimes by Trump, this is as far as Mueller would go: "If we had confidence that the president clearly did not commit a crime, we would have said that," he said, paraphrasing language in his report.

It remains to be seen whether Congress can get any closer to answering that question in a way that would satisfy a public majority.