WASHINGTON - Former special counsel Robert Mueller early Wednesday began his public testimony before the first of two congressional panels about his investigation of President Donald Trump and Russian interference in the 2016 election.

"The president was not exculpated for the acts that he allegedly committed," the former special counsel told the House Judiciary Committee.

Asked by Rep. Jerrold Nadler, D-N.Y, of whether the president could potentially be indicted after leaving office, Mueller responded, "True."

In the first back-and-forth, Nadler, the committee chairman, listed basic yes-or-no questions - or inquiries that could be answered in a few words - to get Mueller to confirm that he did not exonerate Trump.

"Did you actually totally exonerate the president?" the New York Democrat asked.

"No," Mueller said.

"Does that say there was no obstruction?" Nadler said, reading an excerpt from the report where Mueller's team discussed they could not "exonerate" Trump on the matter.

"No."

EMBED: Robert S. Mueller responds to a question

Mueller went on to talk about Justice Department rules that say a sitting president cannot be indicted.

"The report did not conclude that he did not commit of obstruction of justice," Nadler asked again.

"That is correct," Mueller said.

The president has repeatedly claimed the report showed there was "no collusion" and "no obstruction."

Mueller also confirmed that Trump refused to be interviewed by his team.

But Mueller was careful not to be drawn into a statement that Trump committed obstruction of justice. Rep. Hakeem Jeffries, D-N.Y., questioned Mueller about the elements of an obstructive act under criminal law, in an apparent effort to get Mueller to agree with the congressman's own analysis that Trump had done so, particularly when he tried to get Mueller fired.

Mueller agreed that Trump understood he was being investigated, and that he viewed the special counsel's inquiry as detrimental to his interests. But he wouldn't sign onto Jeffries' conclusions that Trump had engaged in all the conduct that one must in order to be charged with obstruction.

"I don't subscribe to the way you analyzed that," Mueller said at the end of Jeffries' questioning. "I'm not saying it's out of the ballpark," he added. "But I'm not supportive of that analytical charge."

The hearing began shortly after 8:30 a.m. Eastern time. Mueller entered the hearing room accompanied by two of his deputies, Andrew Goldstein and James Quarles, who sat behind him.

In his opening statement Nadler praised Mueller's long career of public service, seeking to preempt expected GOP attacks on the war hero-turned-FBI director who has found himself in Trump's crosshairs.

"Your career… is a model of responsibility," Nadler told Mueller, listing his accomplishments as a decorated Marine officer who received a Purple Heart and the Bronze Star while fighting the Vietnam, then led the FBI following the Sept. 11, 2001 terrorist attack.

Nadler said Mueller returned to public service to take up the Russia investigation and "conducted that investigation with remarkable integrity," never commenting on his work in public, "even when you were subjected to repeated and grossly unfair personal attacks."

The committee's top Republican opened by arguing that President Trump is innocent of any wrongdoing, and promised the GOP would look into "how baseless gossip," as he put it, formed the foundation of the special counsel's report.

"The report concludes no one in the president's campaign colluded, collaborated or conspired with the Russians," Rep. Doug Collins, R-Ga. said. He also argued that while Trump had an "understandably negative" view of Mueller's probe, and could have shut it down, he "did not use his authority to close the investigation" because he "knew he was innocent."

Later, Rep. Louis Gohmert, R-Texas, an old nemesis of Mueller's, spent his five minutes on the attack. First, he got Mueller to concede that he and fired former FBI director James Comey "were friends." Then, he tried to suggest that the FBI investigation of the president was politically biased from the beginning.

As Gohmert's tempo quickened and frequently cut off Mueller's attempted answers, the former special counsel asked in frustration, "May I finish?"

Gohmert barreled forward, arguing that, rather than obstruct justice, Trump set out to defend himself from Trump-hating prosecutors and agents.

"What he's doing is not obstructing justice. He is pursing justice and the fact that you ran it out two years means you perpetuated injustice," Gohmert said.

During his questioning, Rep. Guy Reschenthaler, R-Pa., who served as a lawyer in the Navy and later as a judge in Pennsylvania, accused Mueller of including only "the very worst" information about President Trump even though he knew that Trump would not be indicted and that the report would be made public.

"Not true," Mueller replied, in a rare moment of pushback against Republican attacks on his team's integrity.

Mueller said that the team "strove to put in exculpatory evidence" about Trump's conduct. Mueller said the team had to make choices about what to include. He agreed that prosecutors would generally avoid putting damaging information about a person who wasn't being charged. But, he added, "most cases are not done in the context of the president."

In the afternoon, Mueller opened his House Intelligence Committee testimony with a notable correction to a statement he made earlier, suggesting his team would have charged Trump if not for Justice Department legal guidance that prohibits the indictment of sitting presidents.

The suggestion came during an exchange with Rep. Ted Lieu, D-Calif., on the House Judiciary Committee. Mueller was asked if the reason he "did not indict Donald Trump is because of OLC opinion stating that you cannot indict a sitting president."

"That is correct," Mueller said.

That seemed to contradict what Mueller wrote in his report and what Mueller's office had said previously, though Mueller passed an opportunity to clean it up at the earlier hearing. At the Intelligence Committee hearing, though, he returned to that moment.

"That is not the correct way to say it," he said of Lieu's description, adding later, "We did not reach a determination as to whether the president committed a crime.

Mueller has appeared far more forceful and in command. At the outset, he corrected his assertion about Justice Department policy and its affect on a charging decision. He offered an impassioned plea for policymakers to address Russian meddling in the U.S. elections, and he forcefully noted the Russian efforts were not over.

"They're doing it as we sit here, and they expect to do it in the next campaign," he said. He also said that "many more countries" were developing such capabilities.

On several occasions, he also pointedly took issue with Trump's behavior and characterizations of the special counsel's work. At one point, he said that "problematic is an understatement" to describe Trump's favorable comments about WikiLeaks, and he accused the president of "giving some hope or some boost to what is and should be illegal behavior."

Also in the afternoon hearing:

- Mueller agreed with Rep. Adam Schiff's, D-Calif., characterization that seeking campaign assistance from a foreign power was "unpatriotic" and "wrong," and that candidates for high office must be held to a high standard. Mueller had previously said that, in general, accepting assistance from a foreign power is a crime.

Mueller also agreed that when government officials lie, it can open them up to blackmail. Speaking about former national security adviser Michael Flynn's lies to the FBI about his conversations with the former Russian ambassador to the United States, Schiff said the Russians knew about those calls and asked if they could have exposed Flynn's lies. "Yes," Mueller said.

Mueller also agreed that the Russian government could have revealed that Trump wasn't telling the truth about how long into his campaign he had been in talks about a potential real estate deal in Moscow. Schiff called such leverage "the stuff of counterintelligence nightmares," a characterization Mueller didn't dispute. Mueller added that it spoke to the need for a "strong counterintelligence entity" to ward against foreign governments compromising U.S. public officials.

"We are all left to wonder whether the president is representing us or his financial interests," Schiff said.

- Mueller said the special counsel team understood that it "could subpoena the president" but chose not to because they assumed Trump would fight it and extend the investigation for a "substantial period of time."

In his most extensive comments yet on the decision not to compel Trump to sit down for an interview, Mueller conceded the president's written answers to questions - which he ultimately had to settle for in place of an interview - were "certainly not as useful as the interview would be." From the outset, he said, "one of the things we wanted to accomplish in that was having the interview of the president."

But Mueller said negotiations over a sit-down dragged on for more than a year, and "we decided that we did not want to exercise the subpoena powers because of the necessity of expediting the end of the investigation."

Asked if Justice Department officials had somehow undercut his authority to issue a subpoena, Mueller said, "We understood we could subpoena the president."

- Mueller said he found repeated statements by Trump during the campaign praising WikiLeaks to be "problematic" -- his most pointed criticism of Trump's behavior since beginning congressional testimony.

- - -

The Washington Post's Matt Zapotosky, Karoun Demirjian, Rachael Bade, Rosalind S. Helderman, Tom Hamburger, Shane Harris, Devlin Barrett, John Wagner and Rachel Weiner contributed to this report.