Senate at 50-50?.... Recover Soon Tim Johnson!

Sen. Tim Johnson (D-S.D.) underwent emergency surgery overnight after falling ill at the Capitol and was in critical condition early this morning, introducing a note of uncertainty over control of the Senate just weeks before Democrats are to take over with a one-vote margin.

Johnson, 59, was taken to George Washington University Hospital shortly after noon, after becoming disoriented during a conference call with news reporters. He underwent "a comprehensive evaluation by the stroke team," his office said. Aides later said he had not suffered a stroke or heart attack.

Nursing supervisor Quinn Collins said early today that the senator was out of surgery and in critical condition. Hospital officials and Johnson aides offered no further comment or details; a more complete statement was expected later this morning.

The two-term senator's illness -- which sent Senate Democratic leader Harry M. Reid (Nev.) rushing to the hospital to check on Johnson -- underscored the fragility of Democrats' hold on the next Senate, which they won by the narrowest of margins in the Nov. 7 elections. Should Johnson be unable to complete his term, South Dakota's Republican governor, Michael Rounds, would name a replacement for the next two years