Updated at 4:56 p.m. ET

Peril from foreign interference in American elections will persist through the 2020 presidential race, former special counsel Robert Mueller warned on Wednesday.

Asked whether Russia would attempt to attack future U.S. elections, as it did in 2016, Mueller replied: "They're doing it as we sit here."

Mueller didn't detail a prescription for how he believes Congress or the United States should respond, but he recommended generally that intelligence and law enforcement agencies should work together.

"They should use the full resources that we have to address this," Mueller said.

That warning came during hours of hearings, first before the House Judiciary Committee and then the intelligence committee, in which Democrats sought to underscore that Mueller had not cleared Trump of obstruction allegations and that he had found many contacts between Trump's campaign and the Russian interference in the 2016 election.

"Did you actually totally exonerate the president?" asked House Judiciary Committee Chairman Jerry Nadler, D-N.Y.

"No," Mueller said.

The exchange made the point that Democrats have repeated since Mueller filed his report: His findings don't boil down to a vindication or an inoculation for Trump, as the president claims.

What isn't clear is what the exchange will mean in terms of actions by the president's opponents.

Mueller studiously avoided being drawn into questions about prospective impeachment proceedings — which divide the Democrats that control the House majority — although he admitted that a prosecutor still might charge Trump with a crime after he's no longer in office.

Rep. Ken Buck, R-Colo., asked Mueller whether he believed there was sufficient evidence for a charge when Trump no longer enjoys the protection of the Justice Department policy that forbids indicting a president.

Yes, Mueller said. But for the Office of Legal Counsel's opinion that bars charging a president, the former special counsel said to Rep. Ted Lieu, D-Calif., that he and his office might have decided whether to try to bring an indictment against Trump.

Some Democratic presidential candidates have endorsed doing so if they're elected next year, but no president has ever been prosecuted after the fact for actions in office — another political minefield for the party to navigate.

Other Democrats on Wednesday emphasized what they called key findings from the special counsel's investigation, including the details about Trump's then-campaign chairman, Paul Manafort, meeting with a Russian contact who has been linked with Russia's intelligence agencies — and giving him polling and other material from the Trump campaign.

But Mueller also stressed that he would not go beyond what he has already said or written and would not violate the guidelines the Justice Department has imposed on what he can reveal on Wednesday.

Time and time again, he declined to associate himself with whatever characterization was being drawn by a lawmaker questioning him, and on a few occasions, he responded curtly: "I take your question."

Collins and Co. for the minority

Republicans used their time with Mueller to emphasize that the special counsel established no conspiracy between the Trump campaign and the Russian attack on the election.

House Judiciary Committee Ranking Member Doug Collins, R-Ga., sought to underscore the thoroughness of Mueller's report — and the conclusion, supported by that thoroughness, that there had been no conspiracy between Trump's campaign in 2016 and the Russians who interfered in the election.

Other members attacked the former special counsel for what they called malpractice and bias.

Rep. John Ratcliffe, R-Texas, told Mueller that he had failed to fulfill his responsibilities as a prosecutor by writing that he could neither charge Trump nor "exonerate him" — because exoneration is not a prosecutor's job, Ratcliffe said.

His job is to determine whether sufficient evidence exists to bring a charge and, if he can't, not only mustn't he bring the charge, but he also must not reveal what he uncovered because there won't be an indictment, Ratcliffe said.

"You managed to violate every principle and most sacred tradition for prosecutors," the Texas congressman said.

Ratcliffe asked Mueller whether he could cite a written Justice Department policy that permitted the specific actions he had taken with his investigation and his report.

"I cannot," Mueller said, "but this is a unique situation."

Rep. Steve Chabot, R-Ohio, sought to draw Mueller out about some of the more salacious aspects of the Russia imbroglio, including the so-called Russia dossier produced by former British intelligence officer Christopher Steele.

But Mueller wouldn't go there.

He said that matter was being handled by others inside the Justice Department and, at one point, said he didn't know either the names Fusion GPS — the political intelligence firm that commissioned the Steele material — or Glenn Simpson, its founder.

Mueller deferred again in the session with the House intelligence committee to address alternative hypothesis propounded by Ranking Member Devin Nunes, R-Calif., and other members about the early phase of the Russia investigation.

That's also being investigated by others in the Justice Department, Mueller said.

The former special counsel also tried to dispute accusations that members of his team were politically biased because of their work with Democrats or political contributions. Mueller said he picked the most effective people for the job.

The Justice Department calls for officials not to consider employees' political views when hiring or making assignment.

Reluctant witness

The white-haired former G-man hadn't wanted to testify before Congress. He gave many one-word or monosyllabic answers, asked members of Congress to repeat themselves, and frequently responded by saying, "I'd refer you to the report."

Mueller said in a brief statement at the Justice Department earlier this year that his report was his testimony and that he didn't think it would be appropriate for him to star in a big set piece event on Capitol Hill.

The longtime prosecutor also sometimes appeared to struggle to follow which members of Congress were questioning him and he wasn't able to recount precisely, at one point, which presidents in the past had nominated him for which of the roles he has served.

Democrats had insisted that Mueller appear. They negotiated for months and eventually compelled him with a subpoena.

Nadler believed it would be valuable for more Americans to see and hear Mueller on TV describing what he found in his investigation, given that many people haven't read his report.

Mueller documented a vast wave of interference by Russia's government in the 2016 presidential election with the object of hurting candidate Hillary Clinton and helping Trump get elected.

The special counsel's office also documented many contacts between Trump's campaign and Russians during that time but did not establish a criminal conspiracy related to the election.

Rep. Jim Himes, D-Conn., mentioned during the intelligence committee hearing that national security officials — including, earlier this week, FBI Director Christopher Wray — have warned that election interference will continue through the 2020 presidential race.

Knowing what Americans know today, Himes said, should a campaign contacted by foreign agents report that to the FBI?

"It should and it can be — depending on the circumstances — a crime," Mueller said.

As to Trump's praise for WikiLeaks in 2016 while it was revealing politically embarrassing material stolen by Russian government cyberattackers, Mueller was asked about his reaction to those comments.

"Problematic is an understatement," Mueller said.

Volume II of Mueller's report details a number of instances that Democrats and other critics have called obstruction of justice, including attempts by Trump to remove Mueller himself — and then cover up those efforts.

President sanguine

Trump and his aides said beforehand they were unconcerned about Mueller's testimony, and afterward, Trump told reporters that he was feeling good.

"We had a very good day today," the president said as he left the White House for a trip to West Virginia.

The special counsel's office closed without bringing any more criminal charges against Trump's inner circle, and Trump has stressed that he views Mueller's report — which explicitly does not exonerate the president — as an exoneration.

Trump pivoted that talking point slightly on Wednesday — Mueller "didn't have a right to 'exonerate,' " Trump said, picking up the thread from Ratcliffe — and said Democrats "all knew it was phony stuff."

The president said he wasn't concerned about the prospect of an indictment after he's out of office, as Mueller said might be possible, "because nothing was done wrong."

Trump's remarks followed earlier criticism of Mueller by other members of his team.

"This morning's testimony exposed the troubling deficiencies of the special counsel's investigation," Sekulow said Wednesday.

"The testimony revealed that this probe was conducted by a small group of politically biased prosecutors who, as hard as they tried, we're unable to establish either obstruction, conspiracy, or collusion between the Trump campaign and Russia."

Trump had revisited some of his old attacks on Mueller as being "conflicted" and a "never-Trumper" leading up to the testimony and wrote on Twitter that there had been, "NO COLLUSION, NO OBSTRUCTION!"

The president had said he wasn't planning to tune in to see Mueller — and then also said, "Maybe I'll see a little bit of it."

NPR White House correspondent Tamara Keith contributed to this report.

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