President Obama's greatest setback to date has been the 2010 midterm elections. Gains that Republicans scored in the House and Senate still circumscribe his agenda. It is no surprise, then, that the Obama White House wants to achieve something no other president has ever done: Retake full control of Congress in a midterm.
The party of an incumbent president traditionally loses seats in midterm elections. The usual strategy is simply to minimize the damage. Yet Mr. Obama and many Democrats are so buoyed by national polls and the buzz from the November election that they sense a chance to make history by holding their 10-seat Senate majority (counting the two independents who caucus with them) and picking up the needed 17 House seats. That would clear the way for Democratic legislative aims.
A few factors work in the Democrats' favor. After all, the Democratic Senate majority might be secure if for no other reason than the GOP's habit of squandering opportunities by nominating weak candidates. House Republicans are much more unpopular than House Democrats—on average 15 percentage points lower in nine postelection national polls.
Editorial page editor Paul Gigot on the RNC's self-examination. Photo: Associated Press
A grand sweep will be harder than Democrats think, though. Electoral history and the nature of the 2014 races indicate that Democrats actually stand a greater chance of losing the Senate than they do of winning the House.
Since the start of the modern two-party system in the mid-19th century, the party of an incumbent president has never captured control of the House from the other party in a midterm election. While many presidents have held the House for their party, in 35 of 38 midterms since the Civil War the incumbent's party has lost ground.
One reason is turnout. Since 1866, the average turnout rate in presidential elections has been 63%, while it has been 48% at midterm. The drop-off comes disproportionately from the presidential party. Voters from the out-of-power White House party are usually energized—read: angry and eager—to vote against the president, especially by the six-year mark.
Events can encourage voter frustration. Midterm setbacks may be spurred by bad economies, which partly explain losses suffered by the parties of FDR (1938); Harry Truman (1946); Dwight Eisenhower (1958); Ronald Reagan (1982); and Mr. Obama (2010). War fatigue has contributed to other midterm disappointments: LBJ's Vietnam (1966) and Mr. Bush's Iraq (2006). Scandals can take their toll, too, as the GOP's disastrous 1974 Watergate midterm demonstrated.
On the flip side, Americans traumatized by 9/11 rallied around the party of the Republican incumbent in 2002, just as the frustration with efforts to impeach Bill Clinton boosted Democrats in 1998. Even so, history shows that a troubled economy usually trumps everything else.
But don't those polls showing the deep unpopularity of House Republicans mean that Democrats can make up the necessary ground? Not really. Partisan redistricting and an inefficient concentration of the Democratic electorate generally favors the Republicans. Democrats won nearly 1.4 million more House votes than Republicans in 2010 and still lost the House.
Based on historical measures, it would take a massive popular preference for Democrats to overcome their logistical disadvantage, perhaps an almost unheard-of lead of 13 points in the generic ballot questions pollsters use ("will you vote Democratic or Republican for House in the next election?"). Currently, the generic ballot shows a slight Democratic lead of two to three points.
If Democrats do defy history next year, population changes will underlie the move, just as demographics did in the Obama-Romney contest. Smaller midterm electorates are older and whiter than presidential electorates, yet no iron law of politics says they must remain so. Whites now prefer Republicans by as much as 60%-40%, but about 80% of all minorities favor Democrats—and the white proportion of the electorate (both presidential and midterm) has been declining a couple of points every four years.
With each 2% increase in the proportion of minorities in the electorate, Democratic candidates gain a net 1.6% or so of the overall vote. That kind of increase is entirely possible in 2014, when whites may be about 75% of the turnout (down from 77% in 2010) and minorities will likely be about 25% (up from 23%).
Meanwhile, Democrats are focusing their social media and voter-contact technology on engaging minorities and young people to turn out next year. Although Republicans hope to attract more young voters and minorities, and to come closer to matching the Democrats' vote-tech edge, the GOP has a long way to go and relatively little time.
But what if the more competitive chamber in 2014 is the Senate? Democrats are defending seats in seven states that Mitt Romney won in last year's presidential race: Alaska, Arkansas, Louisiana, Montana, North Carolina, South Dakota and West Virginia. Mr. Obama won an average of just 40.5% of the vote in these states. In addition, the retirements of longtime Sens. Tom Harkin (D., Iowa) and Carl Levin (D., Mich.) make those previously safe seats much more competitive. Factor in some freshmen Democratic senators elected from swing states in Obama's 2008 wave (the last time this batch of seats was contested), and Republicans could run competitive challenges in 10 or more Democrat-held seats. Incompetent GOP nominees could change the picture, but almost all of the seats that Republicans are defending are in solid-red states.
The historical Senate midterm dynamic isn't as clear-cut as the one in the House. The president's party has picked up Senate seats in six of 25 midterms since 1914—the first election after the 17th Amendment mandated statewide elections of senators instead of leaving it to state legislatures—but over the past century the president's party has lost an average of about four Senate seats per midterm. Republicans need to net six seats to win control in 2014—precisely the average number of seats gained, in post-World War II "sixth-year itch" elections, by the party not holding the White House.
Playing the averages sets the 2014 scene. Can Republicans match the modern average gain for the opposition party in the Senate in a president's second midterm? Can Democrats greatly exceed the historical average for the president's party in the House? It may be that neither party can meet these expectations. Yet as next year's battle for Congress begins to intensify, the odds favor the Republicans holding the House and getting yet another shot at the Senate.
Mr. Sabato is the director of the University of Virginia Center for Politics and editor of "Barack Obama and the New America" (Rowman & Littlefield, 2013), to which Mr. Kondik, a political analyst at the center, was a contributor.