Control of the U.S. Senate Hasn't Been This Unsteady Since the Post-Civil War Era

From Ronald Brownstein, at National Journal, "THE VOLATILE SENATE":

Instability is a constant in the modern Senate. After the 1980 election, Republicans controlled the chamber for six years (until 1986); Democrats held it for eight (through 1994); and Republicans regained control for six, until the 2000 election divided the chamber exactly 50-50. The next two years saw the parties trading the gavel (as a GOP defector provided Democrats a temporary majority) before Republicans regained control in the 2002 election. But they held that advantage only until 2006, when Democrats won the majority Republicans are now threatening.

This turbulence contrasts with the 26 years of uninterrupted Democratic Senate control from 1955 through 1980. Earlier in the 20th century, Republicans and Democrats each ran off 14-year streaks of unbroken control. From 1895 through 1912, Republicans posted an 18-year reign.

Control of the Senate hasn't been this unsteady since the decades after the Civil War. It's no coincidence that was another period, like ours, of intense economic and social upheaval as America was reshaped by reinforcing waves of industrialization, immigration, and urbanization. And yet even then, the Senate wasn't unstable for as long as it has been since 1980.

The Senate is now flipping so frequently partly because neither party can amass much of a cushion even when it gains control. From 1959 through 1980, the Democrats held a Senate majority larger than 10 seats in all but one of the 11 sessions; since then, the majority party has accumulated an advantage that large only three times in 17 sessions. These thin margins have left the governing party unable "to sustain their majority ... when things go badly," notes Brookings Institution senior fellow Thomas Mann...

More.

Brownstein should know, by the way. He's the author of The Second Civil War: How Extreme Partisanship Has Paralyzed Washington and Polarized America.