WASHINGTON (CNN) -- Telling CNN "we're not changing hands any time soon," a Democratic leadership aide insisted Thursday the newly elected Democratic majority is not in jeopardy, Sen. Tim Johnson's, D-South Dakota, hospitilization.

The aide pointed to several precedents of senators who retained their seats despite taking extended leaves of absence, sometimes lasting for several months and even years.

According to the U.S. Senate Historical Office, three senators have taken extended leaves of absences in the last twenty years alone. In 1991, Arkansas Democratic Sen. David Pryor was absent from the Senate for five months after suffering a heat attack. In 1989, then-Tennessee Democratic Sen. Al Gore left the Senate for a month when his son was involved in a car accident. In 1988, Sen. Joe Biden, D-Delaware, didn't cast a single vote in eight months after he suffered a brain aneurysm.

Since 1942, nine senators have taken extended leaves of absences.

-- CNN's Dana Bash and Ted Barrett