Mid-term elections are problematic for the party holding the Presidency; mid-term elections following scandals or highly divisive policy choices are particularly problematic.
The Republican Party experienced disaster in 1974 following Watergate, the granddaddy of all modern political scandals, losing 49 seats in the House and four in the Senate, giving Democrats a filibuster-proof majority in that body. When Reagan won his second term in 1984 (carrying 49 out of 50 states), the GOP held a 53 to 47 majority in the Senate only to give up 8 seats in 1986 and control to the Democrats following the Iran-Contra Affair.
Bill Clinton sold himself as a New Democrat in 1992, but after seeking to implement Hillarycare and raising taxes, voters sent his party to the cleaners in 1994, with the Republicans gaining back control of the House (in a 54 seat swing) and the Senate (9 seat change) for the first time since the 1950s.
The mid-term elections of 2010 followed a strikingly similar path. After the passage of the Stimulus Bill and Obamacare, the Democrats experienced the greatest reversal of party fortunes in House history. The GOP picked up 63 seats and leadership of the House, as well as 6 seats in the Senate, though Democrats retained control of that body.
Both scandal and unpopular policy choices are once again in the mix as 2014 begins to take shape, and the outcomes in a few key states may change the entire balance of power in Washington.
That Republicans will maintain control of the House seems almost a given with historic trends and their 33-seat majority. All eyes then turn to the Senate, where Harry Reid’s Democrats hold a working 54 to 45 edge (including 2 independents that caucus with them). There are 35 seats up for re-election next year: 21 held by Democrats and 14 by Republicans. Of those, 10 seats appear solidly in play according to the Cook Political Report, and Democrats hold them all. Cook rates three seats “tossup” (Iowa, Montana, West Virginia) and seven “lean Democrat.” The Rothenberg Report lists the same three as “pure tossup” and moves two of Cook’s “lean Democrat” to “tossup/tilt Democrat” (Alaska and North Carolina.)
If Republicans can win the three tossups and pick up only two of the lean/tilt Democrat seats, we'll see a seismic shift in Washington's balance of power. Harry Reid will no longer be majority leader of the Senate, and DC will no longer be a two-thirds Democrat-controlled town.