There is a lesson in this unexpected juxtaposition nevertheless: No nation can safely base its tax and spending plans on inflexible commitments. Political life, both domestic and international, is too unpredictable. Yet U.S. government spending is mostly on autopilot. The government is scheduled to lay out $3.8 trillion this fiscal year -; 70 percent of which will go to mandatory-spending programs, chiefly Social Security, Medicare, Medicaid and interest on the federal debt. Mr. Obama's plan for fiscal 2015 does not change this; it would increase overall spending slightly, paying for it with selected tax increases, while shifting money among priorities here and there. But these tweaks would take place within the same 30 percent of discretionary spending that the current budget contains (3/4).