The discovery of the deadly poison ricin in a Senate office building is a reminder not only of how vulnerable Congress is to terrorism but also of how little lawmakers have done to ensure continuity of government in the event of an attack.

Despite plenty of close calls--a 9/11 jet that was likely bound for the Capitol, the anthrax attacks--both the House and Senate have let more than two years go by without protecting the constitutional system from the widespread incapacitation of lawmakers.

The problem is this: Under the Constitution, each house of Congress requires a quorum of half its members to do any official business. No quorum, no Congress. But there is no provision in the Constitution itself to replace incapacitated members temporarily until they can return.

Thus, if 60 of the 100 senators were in intensive care units with inhalation anthrax or ricin poisoning, or in burn units after an explosion in the Capitol, the Senate would be closed until their return. If a senator faced long-term incapacity, he or she could be expelled by the Senate as a whole--but again, only if a quorum was available. (Expulsion is also a vexing issue: would it be fair or legitimate to expel someone who would recover from a terrorist attack in, say, three months?)

If members of the Senate are killed, they can be replaced temporarily by appointment (usually by governors) thanks to the 17th Amendment; members of the House must be elected, however, so widespread deaths in that body would leave it paralyzed for months until special elections could be held. But neither house is prepared to cope with serious incapacitation.

So what's the solution? We need a new constitutional amendment to allow for emergency interim appointments to the House and Senate in the event that a significant number of legislators are hurt in an attack. The details--how many members have to be incapacitated before interim appointments can take place, for instance--can be worked out by Congress. The form of appointment (by governor or state legislature) can be left to individual states.

In fact, some members of Congress have been working to address this constitutional weakness. Senator John Cornyn, Republican of Texas, has proposed an amendment, as have several lawmakers in the House, including Brian Baird of Washington and John Larson of Connecticut, Democrats both. Sadly, the response from the party leaders in both houses has been deafening silence.

An unwillingness to grapple with these questions is understandable. After all, people often put off writing their wills. Many of us are uncomfortable contemplating our own demise. But members of Congress are different from the rest of us: they have a responsibility not just to their own families but also to the entire country. It's their duty to see to it that the United States government continues to function--no matter what happens.

Norman J. Ornstein is a resident scholar at the American Enterprise Institute.