Discuss as:

More on Johnson

From NBC's Ken Strickland, Mark Murray, and Elizabeth Wilner

Democratic Sen. Tim Johnson of South Dakota has apparently suffered a stroke, two sources tell NBC. Unclear how serious it is. Johnson's office confirms that he was not feeling well this morning and was taken to George Washington University Hospital in DC, where he is being evaluated.

The top concern, of course, is for Johnson and his family, with all of Washington wishing them well. From a procedural standpoint, with control of the currently 51-49 Senate hanging in the balance in the event of a vacancy, reporters are doing due diligence and checking into South Dakota law.

Per South Dakota Secretary of State Chris Nelson, the governor of South Dakota may appoint a replacement if a Senate seat is vacant. The appointment would last until the next general election -- in this case, 2008. Johnson's term happens to expire in 2008, so we would be talking about the remainder of his term. The governor of South Dakota is a Republican, Mike Rounds.

However, this is *if* there's a vacancy. Johnson's seat is not vacant at this time, of course. Nelson says there's nothing in state law that deals with whether one of their members of the Senate is incapacitated. He said the answer would likely come from federal law or the US Constitution.