The Keynesians who now run U.S. policy, at the Treasury and Federal Reserve, have been using their usual demand-side playbook. Bathe the country in government cash, keep interest rates at zero, and the resulting rise in consumer demand will drive everything. They’ve underestimated the supply-chain constraints that have been screaming across the economy for months—from too few workers to the computer chip shortage and soaring lumber and freight prices. The economy can’t produce enough goods and services fast enough to meet the soaring demand from the easing pandemic and government policies that have shoveled cash to consumers and rewarded Americans for not working.