So, how have these economic factors influenced past midterm elections? The obvious example is 2010, when the aftershocks of the 2008 recession helped lead to a surge of tea-party candidates, and led Republicans to gain control of the House, which they still enjoy. Looking at generic vote ballots for this year, Democrats could gain ground in the House of Representatives, but likely not enough to make up their 17-seat deficit. Other economists predict a small swing for House Republicans in 2014 — though nothing approaching the tidal wave of 2010.
Alan Abramowitz, a political scientist at Emory University, says even a stellar economy does not translate into an automatic midterm win for the president's party — there are always intervening factors. "It's not all about the economy," Abramowitz told National Journal. "The one thing is, if you have a recession, the president's party is inevitably going to do badly ... really bad economic conditions are almost always going to hurt the president's party."
Intervening factors — like a hugely unpopular war — can hurt parties as much or more than the state of the economy. In 1966, for example, Democrats lost members in Congress because they had many seats to defend and an unpopular president's war (LBJ, Vietnam) to deal with. Similarly, in 1986 (and 2006, for that matter) it wasn't the economy that hurt Republicans, so much as President Bush's falling approval rating due to an unpopular war in the Middle East.
Going by the systemic factors that influence midterms year in and year out, Republicans seems to have the advantage this year. Republicans are historically more likely to turn out during midterm years, though that effect was suppressed in years where an unpopular Republican was in the White House.
Thomas Mann, a senior fellow at the Brookings Institution, says that while jobs have grown impressively, wages have not. "Whatever happens nationally — which is reflected in presidential job approval and general measures of economic growth and health — is going to play unevenly across these various districts and states," he told National Journal.
Still, most voters have likely already made up their minds about the general state of the economy. "It's late enough now — July — to know that it would be hard to really improve the subjective feelings of voters about how the economy is doing," Mann said.
Another problem for Democrats is that the more seats a party has to defend, the more likely it is to lose. This year, Democrats have to defend 21 seats in the Senate, seven of which are in states that voted for Mitt Romney in 2012. Republicans need to flip just six seats to regain control of the Senate. And thanks to increasing polarization, it's harder than ever to win a district where your party is in the minority.
It's difficult to predict each seat because economic conditions fluctuate from district to district, but despite the general state of the economy — recovering, but slowly — voters generally feel as pessimistic about it today as they did in January. And, perhaps more than any objective economic indices, those subjective feelings give credence to the idea that the Republicans will retain control of the House and gain control of the Senate come next January.