President Donald Trump's campaign to criminally investigate his political adversaries keeps running into an intractable problem: his mouth. The news Sunday that the Justice Department has been secretly weighing charges against Fed Chair Jerome Powell — a frequent target of Trump's attacks — alarmed lawmakers, who called it an effort to weaponize the justice system to affect economic policy. But Trump's freewheeling commentary has gotten in the way of past prosecutions he demanded — and could get in the way this time, too.