Which data?
1960 JFK = 4 years
1964 LBJ = 4 years
1968 Nixon
1972 Nixon
1976 Carter = 4 years
(total 12)
The Republicans won the Senate for 6 years in 1980 on Reagan's coattails, but lost it again to the Democrats in 1986.
http://www.rollcall.com/issues/54_53/politics/29730-1.html?type=printer_friendly
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Prior to 1954, when Democrats took over the House for what turned out to be 40 years and the Senate for 26 years, Congress exhibited a penchant for volatile swings in partisan control. But even during those and other extended periods of a political party’s dominance over either chamber, there have been large gains for the minority, with even generally popular presidents finding themselves rebuffed by the voters in midterm years. [/FONT]