During Mr. Obama’s second term in office (2013-2017), it had become clear that the terms of the public policy debate were undergoing a radical and worrying transformation. In the space of a very short time, certain ideas and policy proposals were being ruled as out of bounds not on the grounds that they were unwise, impractical, or inefficient, but on the grounds that they were products of “disinformation” campaigns on the part of foreign intelligence agencies. To take one example: Those few who publicly expressed reservations with regard to Mr. Obama’s policy toward Russia and Ukraine found...