WASHINGTON — Former special counsel Robert Mueller on Wednesday told Congress that his investigation did not exonerate President Donald Trump, explained why he decided not to consider criminal charges against the president and defended his nearly two-year probe.

"It is not a witch hunt," Mueller said after Intelligence Committee Chairman Adam Schiff, D-Calif., noted that the president had often condemned the probe as just that.

It was a rare flash of emotion from Mueller — and one of the first times he addressed a criticism by the president. He otherwise proved to be taciturn, using his frequently short answers during back-to-back appearance before the House Judiciary and Intelligence committee to confirm a number of damaging facts about Trump uncovered in his investigation into Russian efforts to help the president win his 2016 election.

Mueller's highly anticipated testimony began in the morning with the Judiciary Committee when Chairman Jerry Nadler, D-N.Y., asked the former special counsel if his investigation had indeed cleared Trump, as the president has often claimed.

"No," Mueller answered flatly.

And when asked by Rep. Jackie Spierer, D-Calif., if Russia's help for Trump was a hoax, as Trump often claims, Mueller replied, "It was not a hoax."

The former special counsel, who testified under oath, also detailed why his team didn't decide one way or another whether Trump could be criminally charged, despite some evidence that the White House might have attempted to obstruct his investigation.

"Based on Justice Department policy and principles of fairness, we decided we would not make a determination as to whether the president committed a crime," Mueller said, referring to longstanding Department of Justice Office of Legal Counsel guidelines against indicting a sitting president.

The questioning resumed shortly after 1:00 p.m. before the Intelligence Committee, whose members delved deeper into Russia's interference in the 2016 presidential election.

During testimony before both panels, Mueller discussed what he called Moscow's "sweeping and systematic" meddling in the 2016 election to help Trump.

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

Mueller warned the Russian efforts to disrupt U.S. democracy haven't stopped.

"They're doing it as we sit here," he said. "And they expect to do it during the next campaign"

And the former special counsel criticized Trump for repeatedly praising Wikileaks — "we love Wikileaks," he said on the campaign trail in 2016 — after it published hacked Democratic emails that were later determined to have been stolen by Russia.

"Problematic is an understatement," Mueller said, "in terms of giving some hope or some boost to what is and should be illegal activity."

Mueller, who arrived on Capitol Hill shortly before 8 a.m., told lawmakers on both committees he would not stray beyond the findings of his report, but Democrats are hoping his testimony will make its findings more accessible to millions of Americans who may not have read the document or have tuned out earlier news coverage.