Such behavior is not unusual for presidential candidates — Obama missed a substantial number of Senate votes during his run in 2008. 

The campaign said it will reschedule any canceled events, and return to Iowa to campaign Saturday.

The balanced-budget vote is a largely ceremonial one, as the amendment seems unlikely to pass by the three-fifths majority required in both chambers of Congress. If approved, the legislation would require ratification by three-quarters of state legislatures.