No self-respecting journalist is going to stop using a source because of an instruction from the White House. But the media question of the day is why members of the press corps aren’t deciding on their own to reject the source who seems to have been misleading them for years.

The Washington Post reports that the Trump communications team is urging media outlets to avoid booking House Intelligence Committee Chairman Adam Schiff (D., Calif.), who has long claimed to have seen “more than circumstantial” evidence of Trump-Russia...