Continuity of government
Its an arcane subject that was discussed a month ago on Nightline. The issue is what would be done if Washington DC were hit and much of the Federal Government top level staffing was lost. In the Nightline show, they discussed the plans developed during the Cold War of which some elements went into effect to some extent on 9/11 and afterward.
Today, in this Yahoo! News item reports that the House passed plans for how to reconstitute the legislative branch should an attack kill large numbers of Representatives. Excerpt:
The measure would require special elections within 45 days of the House speaker confirming that a catastrophic event had left at last 100 of the 435 seats vacant. Language was added to ensure that military personnel stationed overseas would have their voting rights protected.
The Senate has not taken up the terrorist attack issue, though Sen. John Cornyn, R-Texas, has proposed a constitutional change giving states the flexibility to come up with their own solutions.