Nicholas Felton

The performance of the economy, it has long been believed, is the key determinant of voting behavior in the midterm elections. For example, the recession of 1982, and a corresponding double-digit unemployment rate, is usually blamed for the twenty-six-seat loss that Ronald Reagan's Republicans sustained in the House that year. Or take 1946, when the economy contracted severely while reorienting itself after World War II and Harry Truman's Democrats lost fifty-four House seats. Dwight Eisenhower's Republicans faced reelection in a recessionary environment in 1958 and lost forty-eight seats; Gerald Ford's, also facing a recession (as well as the stain of Watergate), lost the same number in 1974.

Recent elections, however, have done much to challenge that premise. Bill Clinton helped to create millions of new jobs and pull the economy out of recession, and yet in 1994, his party suffered a catastrophic defeat at the midterms, losing a net of fifty-four representatives and eight senators. George W. Bush, on the other hand, gained eight House seats in 2002 in spite of an economy that had just escaped from a recession and was still shedding jobs.

There are some earlier contradictions, too, when one examines the record more carefully. The economy was extremely strong in 1966, growing at a 6.5 percent clip that year, but Lyndon Johnson couldn't stave off the loss of forty-seven Democratic seats in the House. On the other hand, George H. W. Bush's Republicans lost just eight seats for the party in 1990 in spite of an economy still in the midst of a recession.

Of course, there are alternate explanations in many of those cases: George W. Bush's popularity honeymoon following 9/11 helped his party, while Johnson's getting quagmired in Vietnam hurt his. But this brings me to my larger point: Congressional elections are not all about the economy. Rather, they're all about the president. The correlation between the president's Gallup approval rating immediately prior to the midterms and his party's performance has been very strong. In fact, once the president's approval rating is accounted for, knowing about the economy doesn't tell anything more about how to predict the outcome of the midterms.

This may be disappointing news for the Republicans, who will face a relatively unpopular Democratic Congress and an economy that is unlikely to have fully recovered by 2010. But President Obama — for the time being — remains very well liked. It will not suffice to get Americans to blame Nancy Pelosi for the economy's problems; they will have to blame Obama, too.

There is also a lesson here for the president: Use your bully pulpit to its full advantage. This, indeed, is a lesson that Obama should already have taken to heart. When the White House handed the reins of the stimulus package over to the congressional Democrats in February, it nearly lost control of the bill, with polls showing a sudden and substantial decrease in public sentiment for the measure. But a press conference and a couple of presidential field trips later, the stimulus regained its footing and was passed into law.

All is not lost for the Republicans, however. While a popular president can help his party to stem its losses, his party nearly always loses at least some seats at the midterms. Since World War II, the president's party has lost an average of twenty-four House seats in the interim elections, gaining ground on just two of sixteen occasions. My statistical model shows that Obama will need to sustain an approval rating in the range of 65 percent to avoid losing any ground in the House. (The Senate, where the Democrats can take advantage of at least five Republican retirements, might be a different story.)

Why does the president's party nearly always lose ground at the midterms? One common explanation is that the public has an intrinsic preference for divided government. The problem with this theory is that if it were true, the president's party would also tend to lose ground in the House in presidential election years. But that is not the case. Instead, since 1946, incumbent presidents have seen their parties gain an average of twelve seats in the Congress in years when they sought reelection.

The answer to the riddle may be this: While a president's coattails can be strong at the midterms, they are not as strong as when the president himself is on the ballot. And in fact, the bigger a president's coattails are when he is elected, the more trouble his party tends to have two years later. Therefore LBJ, who had cruised to election by 23 points in 1964, saw his party shed nearly fifty seats two years later. But George W. Bush, who had in fact lost the popular vote in 2000, was one of the few incumbents to see his party gain ground in the subsequent election.

Many of the voters who went to the polls in 2008 did so because of Barack Obama; almost 90 percent of those voters also happened to vote Democratic for Congress. But many of those voters will not turn out next year without a presidential race to pique their interest. Some of the same Democratic representatives who most benefited from Obama's coattails in 2008, then, are also the most vulnerable to an upset. Their fate may depend on how much this president can personalize that election — and, of course, how much he can mobilize his powerful voter-turnout operation for them — and how well liked he can remain. Obama's popularity is the Democrats' greatest asset heading into the midterm elections in 2010 — but it is also in some sense their greatest liability.

Nate Silver runs the political-prediction Web site FiveThirtyEight.com and is an analyst and writer for Baseball Prospectus.

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