For starters, the 2-percent figure is arbitrary.
It doesn’t measure how much a country actually contributes to the common defense.
As The Washington Post has noted, Greece meets the 2-percent threshold because it spends a lot of money on military pensions and on weapons systems aimed at deterring its fellow NATO member, Turkey—neither of which makes America and Europe safer.
Rachel Rizzo, an expert on trans-Atlantic security at the Center for New American Security, told me Germany could reach the 2-percent threshold by giving everyone in its Ministry of Defense a raise. That wouldn’t do much to enhance security either.
But the larger problem with demanding that America’s NATO partners spend 2 percent—or 4 percent—on defense is that it assumes Europe’s biggest threats are military.