The feud that has simmered for months between Congress and the Justice Department erupted this week into a cage match. That’s because the House is homing in on the goods.

Until this week, Deputy Attorney General Rod Rosenstein and fellow institutionalists at the department had fought Congress’s demands for information with the tools of banal bureaucracy—resist, delay, ignore, negotiate. But Mr. Rosenstein took things to a new level on Tuesday, accusing House Republicans of “threats,” extortion and wanting to “rummage” through...