Senator Tim Johnson, a Democrat from South Dakota, was in intensive care today after undergoing surgery late Wednesday night for a brain hemorrhage, a development that highlighted the fragility of the Democrats’ new majority in the Senate.... [HNN: If he dies or resigns, he would be replaced by the Republican governor. The new senator would remain in place until Johnson's term is up in 2008.]

According to information from the Senate historian cited on CQ.com, at least nine senators have taken extended absences from the Senate for health reasons since 1942. Robert F. Wagner, Democrat of New York, was unable to attend any sessions of the 80th or 81st Congress from 1947 to 1949 because of a heart ailment. Senator Joseph R. Biden Jr., Democrat of Delaware, missed about seven months in 1988 after surgery for a brain aneurysm. And David Pryor, Democrat of Arkansas, suffered a heart attack in April 1991 and returned to the Senate in September that year.

[HNN: In 1969 South Dakota Sen. Karl Mundt (R) suffered an incapacitating stroke. He continued to hold the office until the end of his term in 1973.]