They happen whether they are due to our elected leaders failing to reach an agreement regarding the Fiscal Cliff or the credit markets freezing up or a currency crisis or a large hedge fund imploding.
Credit ratings agencies have issued recent warnings to the U.S. that its credit will be downgraded if the fiscal cliff problem is not sufficiently resolved.
Forth, as major holders of US sovereign debt, banks are exposed to credit risk, should interest rates spike as the economy approaches the Fiscal Cliff.