Of Special Counsel Robert Mueller’s many targets, the most tragic may be former National Security Adviser Michael Flynn. The former three-star general pleaded guilty last year to a single count of lying to the FBI about conversations he had with Russia’s ambassador to the U.S. Now we learn from Mr. Flynn’s court filing to the sentencing judge that senior bureau officials acted in a way to set him up for the fall.

Not a rich man after decades in uniform, Mr. Flynn pleaded guilty to avoid bankruptcy and spare his son from becoming...