These unified states: the country's highly polarized politics has significant repercussions for state governments.

• Author: Kurtz, Karl
• Position: LEGISLATURES

The political landscape changed dramatically after the 2012 election. For the first time in more than 50 years, one party controls both chambers of the legislature and the governors' office in 37 states--Republicans in 23 states, Democrats in 14.

"The 2012 election drove home a key political trend: The red states are getting redder and the blue states are getting bluer," says University of Virginia political scientist Larry Sabato. "This is a highly polarized era."

This stark political divide has significant political and policy consequences in highly charged partisan areas such as health care, labor, social issues, immigration and tax policy.

The last time there were this many states under one-party control was during the height of the Cold War and "Communist threat," following Dwight D. Eisenhower's first election as president in 1952. Just about everyone liked Ike, his coattails were long, and Republicans won the majority of state legislatures outside the South.

Following Eisenhower's time in the Oval Office and through the 1970s, the number of "unified governments" declined to about half the states. Then during the mid-'80s through 2004, divided governments were more common than not, with each party controlling at least one chamber or the governorship in more than half the states.

The change in the dominant party has been just about as dramatic. Until 1994, Democrats controlled more states than Republicans, partly because they held the 13 southern states. Since Democrats started losing their dominance in the Solid South in 1994, Republicans have controlled more states after every election except two.

What has brought about this increase in unified governments? According to Sabato, nearly 90 percent of voters identify with or lean toward one party, and increasingly they vote for all or almost all members of that party on Election Day. A 2012 Gallup Poll at the national level showed that a record-high 38 percent of voters preferred that the president and Congress be of the same party. "The electorate itself does what straight-party levers in the voting machines used to do," says Sabato.

The 2012 state elections reflect this party-line voting. In 22 of the 24 states that Governor Mitt Romney carried, Republicans either held on to or gained the majority in both legislative chambers. The exceptions are Kentucky and West Virginia, where Democrats still hold on at the state legislative level against the trend of Republican gains in the South, but voters reliably choose Republicans in presidential elections.

Likewise, Democrats now control or maintained the majority of both houses in 18 of the 26 states President Barack Obama won.

The eight states that voted for Obama but have legislatures at least partially under Republican control are Florida, Iowa, Michigan, New Hampshire, Ohio, Pennsylvania, Virginia and Wisconsin. All were battleground states and could have gone either way in the presidential...