WASHINGTON — For more than two years, Democrats have hoped that Robert S. Mueller III would show the nation that President Trump is unfit for office — or at the very least, severely damage his re-election prospects. On Wednesday, in back-to-back hearings with the former special counsel, that wish could face its final make-or-break moment.

Lawmakers choreographing the hearings before the House Judiciary and Intelligence Committees warn that bombshell disclosures are unlikely. But over about five hours of nationally televised testimony, they hope to use Mr. Mueller, the enigmatic and widely respected former F.B.I. director, to refashion his legalistic 448-page report into a vivid, compelling narrative of Russia’s attempts to undermine American democracy, the Trump campaign’s willingness to accept Kremlin assistance and the president’s repeated and legally dubious efforts to thwart investigators.

For a party divided over how to confront Mr. Trump — liberals versus moderates, supporters of impeachment versus staunch opponents — the stakes could scarcely be higher.

“One way or the other, the Mueller hearing will be a turning point with respect to the effort to hold Donald Trump accountable for his reckless, degenerate, aberrant and possibly criminal behavior,” said Representative Hakeem Jeffries of New York, the House Democratic Caucus chairman and a member of the Judiciary Committee. “After the hearing, we will be able to have a better understanding of the pathway forward concerning our oversight responsibilities and the constitutional tools that are available to us.”