The United Nations is failing abysmally, and dangerously, in its mission. Founded in 1945 as a vehicle to avert war and promote human dignity and freedom, the U.N. has instead become a self-serving and ever-expanding haven of privilege for the world’s worst regimes, rife with bigotry, fraud, abuse, and corruption, both financial and moral. Yet the American foreign policy community treats it as taboo to speak seriously about sidelining, supplanting, or leaving the U.N. The usual argument is that...