Chief of Staff John Kelly is by all accounts imposing more discipline in the Trump White House, but a mini-drama of the last week shows there’s still more clean-up duty to be done. To wit, notice the alt-right brigades who seem to rise up as if on call to smite some White House policy opponent of aide Steve Bannon.

The latest target has been H.R. McMaster, the three-star general who took over as national security adviser after President Trump fired Michael Flynn. Lt. Gen. McMaster has come in for abuse for favoring more troops...