The most dangerous domestic problem facing America’s federal government is the rapid growth of its budget deficit and national debt.

According to the Congressional Budget Office, the deficit this year will be $900 billion, more than 4% of gross domestic product. It will surpass $1 trillion in 2022. The federal debt is now 78% of GDP. By 2028, it is projected to be nearly 100% of GDP and still rising. All this will have very serious economic consequences, and the CBO understates the problem. It has to base its projections...