South Dakota state law says that the governor can appoint a replacement when there is a "vacancy," but Secretary of State Chris Nelson tells CBS News political producer Steve Chaggaris that it's unclear whether a seat held by an incapacitated senator would be considered "vacant."

Unless Johnson dies, the state of South Dakota is unsure of how to proceed if he's incapacitated. If he dies, however, the governor, Mike Rounds, would appoint a replacement who would serve until the next general election in 2008, Chaggaris explains.

It was my understanding that the Senate gets to determine if and when a Senator is physically or mentally incapcitated, and therefore cannot serve, and that, historically, that body hasn't been all that concerned to get too close to the subject -- if the Senator wanted to serve, and could get to the chamber, that was sufficient. Perhaps I'm wrong about that -- I'm sure knowledgeable people will be writing volumes on the subject soon.

(U.S. Constitution, Article 1, Section 5: Each House shall be the Judge of the Elections, Returns and Qualifications of its own Members, and a Majority of each shall constitute a Quorum to do Business; but a smaller number may adjourn from day to day, and may be authorized to compel the Attendance of absent Members, in such manner, and under such Penalties as each House may provide.

Each House may determine the Rules of its Proceedings, punish its members for disorderly Behavior, and, with the Concurrence of two thirds, expel a Member.)

Oh, one other thing. I hope that one possibility is being given due consideration by the people examining Senator Johnson, and it's an indication of just how far down the rabbit hole we've fallen that I would think it necessary to say this: they would be well advised to do a thorough physical and toxicological examination for any possible sign of an external cause for Johnson's condition.

I'm just saying.

Update: Philip Klinker, posting on Polysigh, seems certain of his interpretation of the relevant South Dakota law. According to Klinker, the temporary Senator appointed by the Governor would be replaced by the winner of a special election. If the next general election was scheduled within six months of the appointment, the special election would be held at the same time, otherwise the special election would be held 80 to 90 days after the appointment. This means that the temporary replacment would serve for a maximum of 6 months. However, there's still no information on what constitutes a "vacancy" and who gets to determine when a vacancy has occurs. I think everyone seems clear that the death of a Senator creates a vacancy, but whether physical or mental incapacoty does, and who gets to judge the level of incapacity, is still not clear to me.

Update: According to news reports, Johnson had a congenital malformation which caused tangled blood vessels. He had emergency brain surgery to drain the accumulated blood. At the last report I've seen, he was in stable but critical condition.

Given that, my foray into conspiracy-paranoia was unfounded. I hope that, for his sake and for ours, Senator Johnson has an uneventful and successful recovery.

Update: Blue Girl, Red State has more light, less heat.

More here.