Neither president paused to consider whether and how the clumsy tools of government could actually fulfill these dreams. Kennedy took the first steps into a war in Vietnam -- which proved that supporting friends did not assure the success of liberty and that there were some burdens Americans would not bear.
When Johnson signed the Economic Opportunity Act, he proclaimed that it represented nothing less than "a commitment to eradicate poverty." But biographer Robert Dallek wrote that the president "was clueless as to just how the program would work." Like many Great Society programs, it did not live up to its billing.
Neoconservative thinkers have long revered Kennedy for his belief in using military power to propagate democracy and human rights abroad, even in places where they were unlikely to flourish. There is a straight line from his inaugural address to our invasion of Iraq and our protracted presence in Afghanistan, both costly, high-minded adventures with meager payoffs.
JFK's domestic plans provided the inspiration for Johnson's Great Society, which likewise attracted plenty of overconfident intellectuals. "In 1962," wrote Dallek, "a group of University of Michigan social welfare experts predicted that it would be relatively easy to end poverty in America at a cost of $2 billion a year, less than 2 percent of GDP."
Today, we spend triple that amount, 6 percent of GDP, and poverty has yet to be ended. In 2012, the Census Bureau says, nearly 50 million Americans -- 16 percent of the population -- were poor even after it counted the various forms of government aid they get.
JFK and LBJ set out to prove how much the U.S. government could accomplish at home and abroad, a mission that endeared them to those who believe in the promiscuous use of power. They ended up proving how much it could not accomplish, and how little extravagance can buy.