Democrats are hoping that former special counsel Robert Mueller's public testimony will finally lead to the tidal wave of opposition to President Donald Trump that the initial release of the lengthy Russia report failed to create.

Their biggest obstacle might be Mueller himself.

Mueller is set to answer questions in public on Wednesday for the first time since he took over the Justice Department's probe of Russian election interference more than two years earlier.

The historic hearings before two House committees come months after the release of Mueller's final report on Russia's interference in the 2016 presidential election and its possible coordination with the Trump campaign as well as possible obstruction of justice by the president himself.

But the tight-lipped, famously disciplined former FBI director has already made clear that he has no desire to venture beyond the 448 pages of his Russia report when he speaks to Congress. And that poses a challenge for Democrats, who want Mueller to expose the general public to the most damning findings of his dense report but also want to push him to speak more broadly.

"There are questions that we have that go beyond the report, and there is no legal prohibition on his answering them, so there may be areas that go beyond the report," said Intelligence Committee Chairman Adam Schiff, D-Calif., in an interview with The Atlantic.

"It is our hope that we can inform the American people of the full facts, that they can appreciate the degree to which the Russians interfered in a presidential election to help Donald Trump, the degree to which the president welcomed that help, knew it was going on, welcomed it, and then lied about it and covered it up," Schiff said.

Republicans, meanwhile, plan to grill Mueller about accusations of political bias in the government and on his own investigative team, stretching back to the origins of the Russia investigation.

"What I'm really interested in with Mueller is just the start of the investigation," said Rep. Guy Reschenthaler, R-Pa., in a Fox Business interview.

"I'm very troubled by the fact that the Obama administration weaponized the FBI and they used the FBI to spy on a political campaign," he said. "That's really troubling to me."