WASHINGTON — Special counsel Robert Mueller's report failed to address crucial questions about President Donald Trump's relationship with Russia that the FBI may still be investigating, the chairman of the House Intelligence Committee said Wednesday as he kicked off a hearing designed to spotlight those issues.

"Of all the questions that Mueller helped resolve, he left many critical questions unanswered — what happened to the counterintelligence investigation?," Rep. Adam Schiff, D-Calif., said as he opened a hearing on counterintelligence issues. "Were there other forms of compromise, like money laundering, left out, uninvestigated or referred to other offices? Were individuals granted security clearances that shouldn't have them? And are there individuals still operating in the administration that leave America vulnerable?"

Schiff said he is determined to get to the bottom of those questions, but he wasn't likely to do so at Wednesday's hearing, which featured testimony from two former FBI counterintelligence officials and a conservative commentator.

The former FBI officials, Stephanie Douglas and Robert Anderson, each ran the FBI's National Security Division, a job that entails hunting for Russian spies in the United States. Neither of them is in a position to know what the FBI is doing now, but they sought to interpret the spare language of Volume One of special counsel Mueller's report, the section that details more than 100 contacts between the Trump campaign and Russians.

Douglas, for example, said that when then-Trump campaign chairman Paul Manafort handed polling data to a person the FBI said was linked to Russian intelligence, that amounted to the Russians "tasking" Manafort, a term spy hunters use to describe the actions of people under the influence of a spy service.

Manafort was charged with acting as an unregistered agent for Russian-backed Ukrainian politicians, but Mueller made no allegation against him or any other American of acting on Russia's behalf in Russia's operation to interfere in the 2016 election. To the contrary, Mueller did not find enough evidence to file criminal charges in any of the contacts between the Trump campaign and Russians.

But Mueller's report was a prosecutor's brief, written under strict Justice Department regulations. It did not render a judgment on the propriety of a major political campaign flirting with a foreign adversary that was offering assistance. Nor did it assess whether U.S. national security was harmed, or whether Trump or anyone else was compromised by his dealings with Russia, including his effort to build a hotel tower in Moscow that would have required the approval of President Vladimir Putin.

"It may not be a crime to build a Trump Tower in Moscow," Schiff said. "Or for [former Trump attorney] Michael Cohen to seek the Kremlin's help to do so. It may not be a crime to try to enrich yourself with a foreign business deal even while running for president, or to lie about it to the American people. But it is deeply compromising."

Schiff and the former FBI officials noted that the Mueller report says FBI agents who worked alongside the Mueller team sent counterintelligence reports back to headquarters, the contents of which are not included in the Mueller report.

Former FBI Deputy Director Andrew McCabe said earlier this year that he opened a counterintelligence investigation into Trump after Trump fired then-FBI director James Comey and boasted about it to Russian officials in the Oval Office. Later in the hearing, Schiff said he has yet to be briefed by the FBI on the status of that investigation, despite repeated requests. He threatened to subpoena the FBI if the bureau continued to resist a briefing.

The Republican witness at the hearing, Andrew McCarthy, a former federal prosecutor who writes for National Review, testified that members of the Trump campaign should have called the FBI when Russians approached them with offers of assistance.

But Republican lawmakers dismissed any notion that the Trump campaign behaved inappropriately. The real scandal, they said, was that the FBI opened a counterintelligence investigation into an American political campaign.

Rep. Devin Nunes of California, the ranking Republican on the committee, called the Mueller report "a shoddy political hit piece."

Schiff sees it much differently.

"Volume I of the report outlines a 'sweeping and systematic' effort by Russia to interfere in the 2016 election for the benefit of Donald Trump," he said. "It establishes that the Trump campaign welcomed the Russian interference because it 'expected it would benefit electorally from information stolen and released through Russian effort.' It shows how the Trump campaign built the theft and dumping of the Russian stolen documents into its campaign messaging and strategy. And as the special counsel made clear, it sets out in great detail why the conduct in his report should concern every American."