If you don't count Clint Eastwood, whose rambling, Bob Newhartesque conversation with an empty chair included implicit criticism of the wars in Iraq and Afghanistan, Rand Paul may have been the only speaker at the Republican National Convention last week who questioned his party's mindless militarism. The Kentucky senator said "Republicans must acknowledge that not every dollar spent on the military is necessary or well-spent."

That mild rebuke—which came, fittingly enough, from the son of the Texas congressman whose resistance to promiscuous interventionism distinguished him from the other contenders for the GOP's 2012 presidential nomination—was no match for the foreign policy vision endorsed by the rest of the speakers, which amounted to a full-throated declaration of war on tyrants throughout the world. This view of America as the righter of all wrongs is hard to reconcile with Republican promises of fiscal responsibility.

John McCain, the GOP standard-bearer in 2008, posited in his convention speech that "it is our willingness to shape world events for the better that has kept us safe, increased our prosperity, preserved our liberty, and transformed human history." The Arizona senator called not only for a continuing occupation of Afghanistan but also for U.S. intervention in Iran, Syria, and every other place where "people are seizing control of their own destinies" by "liberating themselves from oppressive rulers."

Former Secretary of State Condoleezza Rice likewise argued that the United States, through military force and foreign aid in support of "free peoples" and "fledgling democracies," must "sustain a balance of power that favors freedom." Conceding that "there is weariness, a sense that we have carried these burdens long enough," she warned that the alternative is "chaos."

At the same time, Rice worried that "when the world looks at us today, they see an American government that cannot live within its means." Might that perception have something to do with the American government's unbounded understanding of its role in the world?

So-called defense spending by the U.S. government accounts for one-fifth of the federal budget and more than two-fifths of all military spending, nearly 10 times our country's share of the planet's population. With a national debt the size of the national economy and a federal government that borrows 35 cents of every dollar it spends, we cannot afford to police the world in the way that McCain and Rice demand.

The GOP's presidential candidate seems to share this dangerously broad conception of national defense. Like McCain, Mitt Romney criticizes President Obama for supposedly endangering the country with spending "cuts" that let the Defense Department's budget, which has almost doubled in the last decade, continue to rise, albeit at a slower pace. McCain arbitrarily insists that "core defense spending" should never fall below 4 percent of GDP, no matter what threats the country faces or how much it costs to protect against them.

At last week's convention, Romney promised to maintain "a military that is so strong no nation would ever dare to test it." The U.S. currently spends five times as much on defense as China, its closest competitor. Surely there is room for cuts, even by Romney's standard.

Paul Ryan, whom Romney picked as his running mate largely on the strength of his reputation for fiscal conservatism, told the convention "we need to stop spending money we don't have." But the Wisconsin congressman also suggested that a Romney administration would defend every democrat and defeat every dictator. "Wherever men and women rise up for their own freedom," he promised, "they will know that the American president is on their side."

Contrary to Romney and Ryan's implication, Democrats are perfectly capable of reckless military interventions that have nothing to do with national defense, as Obama proved with his illegal air war in Libya. The real puzzle is why Republicans think that being quick to risk other people's lives and squander their money is a mark of courageous leadership.