America’s patron saint for bipartisanship, Arthur Vandenberg, was far from saintly in his personal life. This nasty, petty, egotistical, womanizing, isolationist Michigan Senator from 1928 to 1951 did good: His conversion to interventionism helped ennoble American politics and win the Cold War.

Johnny-one-note historians, who reduce history to punchlines, claim Vandenberg’s isolationism ended when the Japanese bombed Pearl Harbor in 1941. But Vandenberg delivered his interventionist manifesto, which was so revolutionary it was called the “speech heard round the world,” three years later on Jan. 10, 1945. That day, this foe of Franklin Roosevelt endorsed Roosevelt’s foreign policy; this zealot for Congressional prerogatives supported expanding presidential power; and this isolationist endorsed America’s participation in the United Nations. “World War II has put the gory science of mass murder into new and sinister perspective,” he reasoned. “Our oceans have ceased to be moats which automatically protect our ramparts.” Facing such threats, he said: “The commander in chief should have instant power to act.”

Born poor in Grand Rapids, Michigan, in 1884, Vandenberg became a millionaire publisher of the Grand Rapids Herald. He gained the inside track to incumbency by being appointed to complete a Senate term in 1928, then won three subsequent campaigns. In the 1930s, he was a rare effective Republican opposition voice in Washington. He combatted Franklin Roosevelt’s New Deal domestic policy as too expansive, expensive, and centralized. In 1934, he and Senator Joseph Nye condemned America’s participation the Great War as a great betrayal, a scam.

Ignoring America’s tortured debate over joining what became World War I, Vandenberg and Nye offered a simple—and simplistic—explanation: profiteering munitions manufacturers misled America. This conspiratorial analysis dulled the all-American idealism of these supposedly hyper-patriotic “America Firsters.” And it numbed them to Adolf Hitler’s evil and Imperial Japan’s danger.

Still, Vandenberg did not have a foxhole conversion after Pearl Harbor. He continued berating Roosevelt as manipulative and incompetent, condemning Roosevelt’s “private war” and “secret diplomacy.” He claimed America’s “dogmatic diplomatic attitudes” drove Japan “needlessly into hostilities.” ...