Capitol Hill (AP) -- South Dakota Democratic Senator Tim Johnson is being checked out at a Washington hospital after suffering a possible stroke.
A statement issued by his office said he's been taken to George Washington University Hospital, where he is undergoing a comprehensive evaluation by the stroke team.
Johnson turns 60 later this month.
If he were to become unable to serve, it could halt the scheduled Democratic takeover of the Senate. South Dakota's governor, who would appoint any temporary replacement, is a Republican.
Democrats are scheduled to hold a narrow 51-to-49 margin as a result of last month's election.
Johnson is in his second term and is one of the more reserved members of the Senate, rarely taking center stage at news conferences.
Copyright 2006 by the Associated Press. All rights reserved.