Madison, Wis., may be the austerity debate’s central front, but San Juan is an important, if overlooked, battleground. For the past three years, Governor Luis Fortuño has been the Caribbean’s Scott Walker — and like Walker, he’s under siege. When Fortuño began his term, Puerto Rico was an economic mess. Fifteen percent of the island territory’s labor force was unemployed. Facing a $3.2 billion budget deficit, Fortuño implemented deep cuts, slashing public jobs and salaries across the board. The government unions erupted. Thousands of public workers protested Fortuño’s reforms on the streets of San Juan. And in five months, when...