WASHINGTON, D.C. — Robert S. Mueller III appeared hesitant and even shaky at times in his first congressional testimony on the Russia investigation, but the former special counsel still delivered a harsh blow to President Donald Trump’s claims that he was fully cleared of any wrongdoing.

Mueller, 74, provided mostly staccato answers to inquiries from Democrats and Republicans, who tried to maximize their limited opportunity to interrogate the former FBI director about what he did and did not do during his historic investigation of the White House.

“Did you actually totally exonerate the president?” Rep. Jerrold Nadler, a New York Democrat and chairman of the Judiciary Committee, asked.

“No,” Mueller responded. He then said Trump could potentially face charges for obstruction of justice or other crimes after leaving office.

Citing his report, Mueller said Justice Department guidelines that bar indictment of a sitting president had helped shield Trump from potential prosecution.

“I’d like to ask you the reason, again, that you did not indict Donald Trump is because of the (Office of Legal Counsel) opinion stating that you cannot indict a sitting president, correct?” asked Rep. Ted Lieu, D-Calif.

“That is correct,” Mueller said in what appeared a shift from his explanation in his written report.

He later offered a “correction,” however, saying he had incorrectly told Lieu that he didn’t charge the president with a crime specifically because of the OLC opinion.

“That is not the correct way to say it,” Mueller said. “We did not reach a determination as to whether the president committed a crime.”

Democrats and Republicans took turns trying to push Mueller to go beyond the written record —without any notable success — during a contentious Judiciary Committee hearing that stretched to almost four hours.

After a brief break, Mueller began testifying before a second panel, the House Intelligence Committee, for a two-hour session that will focus more squarely on Moscow’s meddling in the 2016 election.

Mueller made clear he views the Russian intelligence operation, which hacked and leaked Democratic Party emails and used disinformation on social media to target voters, as a direct threat to American democracy.

“Over the course of my career, I’ve seen a number of challenges to our democracy,” Mueller said. “The Russian government’s effort to interfere in our election is among the most serious.”

Democrats organized the back-to-back, nationally televised hearings to highlight details from Mueller’s 448-page report, a redacted version of which was released in April.

The investigation found that Trump’s campaign welcomed Moscow’s interference even though it did not establish a criminal conspiracy with the Russians. It also chronicled Trump’s attempts to block or restrict Mueller’s work, episodes that Democrats have described as clear examples of obstruction of justice.

Some of Mueller’s responses could prove helpful to Democrats who hope to start impeachment proceedings against the president. But he often stopped short of supporting their attempts to paint a larger narrative about Trump’s conduct, preferring to hew tightly to the wording of his report and simply refusing to answer dozens of questions.

For example, Rep. David Cicilline, D-R.I., asked Mueller about Trump’s effort to have Corey Lewandowski, his former campaign manager, tell Jeff Sessions, then the attorney general, to limit the investigation to only future cases of foreign interference.

Mueller confirmed various details with monosyllabic answers — “true” or “yes” — but balked when Cicilline tried to string them all together.

“I’m not going to adopt your characterization, but I would say the facts that are laid out in the report are accurate,” he said.

Mueller did not want to testify on Capitol Hill — he only agreed after Democrats issued him a subpoena — and his reluctance occasionally showed in his clipped answers.

At times, he appeared to struggle to hear the questions, asking lawmakers to repeat their questions. He, in turn, was reminded more than once to speak into the microphone so others could hear him.

Republicans largely played to Trump’s base by defending the president and attempting to undermine Mueller’s credibility and that of his investigation.

Rep. Doug Collins of Georgia, the judiciary panel’s top Republican, pressed Mueller about whether Trump was involved in the “underlying crime” of Russian meddling.

“We found insufficient evidence of the president’s culpability,” Mueller said.

Several Republicans criticized the former special counsel for drafting a lengthy report, which they said exceeded his mandate as a prosecutor tasked with black-and-white decisions about whether to bring charges.

Rep. Guy Reschenthaler, R-Pa., said it “flies in the face of American justice.”

Several Republicans accused Mueller of overstepping his bounds by declaring that Trump was not exonerated.

“The bedrock principle of our justice system is the presumption of innocence,” said Rep. John Ratcliffe, R-Texas. “Everyone is entitled to it, including sitting presidents.”

Rep. Tom McClintock, R-Calif., described the report as an overtly partisan statement intended to undermine the president.

“It’s starting to look like, having desperately tried and failed to make a legal case against the president, you made a political case instead,” he said. “You put it in a paper sack, lit it on fire, dropped it on our porch, rang the doorbell and ran.”

Although Mueller did little to push back on most Republican criticisms, he grew animated at McClintock’s characterization and flatly rejected it.

“I don’t think you have reviewed a report that is as thorough, as fair, as consistent as the report that we have in front of us,” he said.

Mueller also rejected Republican accusations that he staffed the special counsel’s office with Democrats who were determined to take down the president.

“I have been in this business for almost 25 years, and in those 25 years I have not had occasion once to ask somebody about their political affiliation,” said Mueller, who headed the FBI for 12 years and served a senior Justice Department official before that. “It is not done.”

Before the hearing started, Trump was firing off his own complaints about Mueller.

“So Democrats and others can illegally fabricate a crime, try pinning it on a very innocent President, and when he fights back against this illegal and treasonous attack on our Country, they call It Obstruction? Wrong!” he tweeted. “Why didn’t Robert Mueller investigate the investigators?”

The special counsel’s office ultimately charged 34 people, including 25 Russians.

Among those charged were Trump’s former campaign chairman, Paul Manafort; his former national security adviser, Michael Flynn; and his former lawyer and fixer, Michael Cohen. Manafort was convicted at trial, while Flynn and Cohen pleaded guilty.

Roger Stone, Trump’s longtime political adviser, is scheduled to stand trial in November on charges of lying to Congress about his conversations involving WikiLeaks. Stone has pleaded not guilty.