In the summer of 1974, Richard Nixon was under great strain and drinking too much. During a White House meeting with two members of Congress, he argued that impeaching a president because of “a little burglary” at the Democrats’ campaign headquarters was ridiculous. “I can go in my office and pick up the telephone, and in 25 minutes, millions of people will be dead,” Nixon said, according to one congressman, Charles Rose of North Carolina.

The 37th president was likely trying to convey the immense burden of the presidency, not issue a direct threat, but he had already made perceived irrationality—his “madman theory”—part of U.S. foreign policy. He had deployed B-52s armed with nuclear bombs over the Arctic to spook the Soviets. He had urged Henry Kissinger, his national security adviser, to “think big” by considering nuclear targets in Vietnam. Then, as his presidency disintegrated, Nixon sank into an angry paranoia. Yet until the moment he resigned, nuclear “command and control”—the complex but delicate system that allows a president to launch weapons that could wipe out cities and kill billions of people—remained in Nixon’s restless hands alone, just as it had for his four post–World War II predecessors, and would for his successors.