(Photo: AP/Tom Lynn) Democratic presidential candidates Senator Bernie Sanders and Hillary Clinton walk on stage before the February 11 debate in Milwaukee. W hen the nation’s top infrastructure analysts calculate the cost of the coast-to-coast investments that the United States needs to make in the country’s highways, bridges, dams, mass transit, and water networks, they end up with a number that few minds can grasp. The American Society of Civil Engineers (ASCE) recently issued its quadrennial rundown on the state of the country’s infrastructure. It is a sobering list of dollar signs. To get the country’s drinking water pipes in good working order could cost more than $1 trillion; “high hazard” dam repairs, $21 billion; major urban highways upgrades, $170 billion; deficient bridge replacements, $76 billion. Adding in mass transit, wastewater, hazardous waste disposal, aviation, and other demands means that the U.S. would have to spend an estimated $3.6 trillion by 2020 just to get...