One of the reasons for the success of the Swiss debt brake is the provisions for a carefully designed emergency fund and escape clause that allows for spending in excess of that permitted by cyclically adjusted revenues (Geier 2011, 2012).
Fiscal rules in the U.S. have failed in constrain spending in the long term, and a major flaw has been emergency expenditures. This design flaw can be traced to the first comprehensive fiscal rule, the Balanced Budget and Emergency Deficit
What Have we Learned from the European Experience with Emergency Funds and Escape Clauses Beljean, T., and A. Geier. (2013). The Swiss debt brake- has it been a success? Swiss Journal of Economics and Statistics, Vol. 149 (2) 115-135. Bodmer,
Under current law, the caps imposed on spending have often been waived in order to fund emergency expenditures. For example, the spending caps imposed by the Budget Enforcement Act of 1990 have been waived for disaster relief, military spending, overseas