Defense alliances are complicated things, but in the U.S. we have bipartisan clarity on one thing: Our allies are letting us down.

"If Saudi Arabia was without the cloak of American protection," Republican front-runner Donald Trump said this weekend, "I don't think it would be around." He has also shamed America's top defense partners in Asia: Japan and South Korea. "We have 28,000 people on the border separating South Korea from this maniac in North Korea. We get nothing," he said. "We get nothing. They're making a fortune."

President Barack Obama has a cooler demeanor, but the same icy attitude toward long-standing military partners. "Free riders aggravate me," he told the Atlantic's Jeffrey Goldberg, not long after informing U.K. Prime Minister David Cameron that the longtime "special relationship" between the nations was at risk unless the Brits met the NATO goal of spending 2 percent of GDP on the military. He also accused the Gulf Arab nations of "pushing us to act but then showing an unwillingness to put any skin in the game."