MANY PEOPLE who viewed Donald Trump as unprepared and temperamentally ill-suited to be president initially reassured themselves that a sober-minded Republican majority in Congress would restrain him. Speaker Paul D. Ryan’s (R-Wis.) pitiable farewell this week spotlighted the emptiness of those hopes. Mr. Ryan allowed the president and his allies to corrupt the House Intelligence Committee and treat federal law enforcement as an enemy. Like Senate Majority Leader Mitch McConnell (R-Ky.) and most other ostensible GOP leaders, Mr. Ryan abetted the president as he sought, fruitlessly, to use fear and bigotry to preserve the House Republican majority in the 2018...