WASHINGTON — President Trump was probably never going to be impeached by the House of Representatives before the 2020 elections. The testimony by Robert S. Mueller III, the former special counsel, makes that a near certainty.

The absence of an electrifying Washington moment in Wednesday’s two-stage testimony by Mr. Mueller not only deprived Democrats of the crystallizing episode they needed to drive public opinion on impeachment, but it also meant Republicans had no reason to budge from their anti-impeachment stance. Pressure will continue from the left and could become so irresistible that the Judiciary Committee begins what it will call an impeachment inquiry, without a formal House vote.

But that is very different from a vote in the full House to formally declare that an elected president had committed high crimes and misdemeanors, for only the second time in history. (Andrew Johnson wasn’t elected.)

Pro-impeachment Democrats have always labored under the burden of Mr. Trump’s iron-fisted control over his own party. Breaks in the ranks of the president’s party always drove major congressional White House investigations in the past, including Watergate, Iran-contra and the impeachment of President Bill Clinton. Thirty-one Democrats voted with Republicans in October 1998 to open an impeachment inquiry into Mr. Clinton.