But the subject matter will probably have to be bigger than the Ukraine phone call, which is not, as some have said, too complicated for the American people to understand, but easy to understand. An American ally needed money, and its new leader needed a meeting with the American president to bolster his position back home. It was made clear that the money and the meeting were contingent on the launching of a probe politically advantageous to Mr. Trump and disadvantageous to a possible 2020 rival.

Everyone gets it, most everyone believes it happened, no one approves of it—but it probably isn’t enough. People have absorbed it and know how they feel: It was Mr. Trump being gross. No news there.

Truly decisive testimony and information would have to be broader and deeper, bigger. Rudy Giuliani’s dealings with Ukraine? That seems an outgrowth of the original whistleblower charges, a screwy story with a cast of characters— Lev Parnas and Igor Fruman, natives of Ukraine and Belarus, respectively, who make you think of Sen. Howard Baker’s question to the Watergate bagman Tony Ulasewicz: “Who thought you up?”

More important will be a text or subtext of serious and consistent foreign-policy malfeasance that the public comes to believe is an actual threat to national security. Something they experience as alarming.