Democrats are still reeling from Special Counsel Robert Mueller’s conclusion that the Trump campaign did not collude with Russians in 2016. But they’ve now hit upon a political comeback strategy: Accuse Attorney General William Barr of a coverup.

That’s the context for Wednesday’s decision by House Democrats to authorize subpoenas, on a partisan vote, demanding that Mr. Barr immediately hand over the entire Mueller report and its supporting evidence. This is intended to give the impression, abetted by a press corps that was...