According to Sam Wang, the Princeton professor of neuroscience and co-founder of the Princeton Election Consortium, the ongoing government shutdown has placed the Republican Party's hold on the House of Representatives in doubt.
Relying primarily on polling by the left-leaning Public Policy Polling — which, Wang takes care to note, had the best record of all major polling firms for the 2012 election — Wang writes in the Washington Post that "If the election were held today, Democrats would pick up around 30 seats, giving them control of the chamber."
Wang goes on to acknowledge that the midterm election is more than a year away, and that much could change in the time between now and then. Nevertheless, he finds that, at a minimum, Democrats are likely to gain seats in 2014, and thus buck the historical trend of the president's party losing during the midterms.
Note that in these calculations I did not even include the worst of the news for Republicans. In a followup series of questions, PPP then told respondents that their representative voted for the shutdown. At that point, the average swing moved a further 3.1% toward Democrats, and 22 out of 24 points were in the gray zone. That would be more like a 50-seat gain for Democrats - equivalent to a wave election.
Of course, the big question is how the current snapshot, a probable House turnover to the Democrats, will evolve in the coming 12 months. At the moment we are in territory that resembles 1995, a shutdown with blame going largely to congressional Republicans. If the government is funded with a continuing resolution (CR), then opinion could easily swing back and the GOP could hold on to the House. But what if the government hits the debt ceiling? In such an extreme circumstance, which has been called the domestic equivalent of the Cuban Missile Crisis, the outcome I have calculated here becomes quite a plausible scenario.
At this point, an analyst would have to be crazy to predict that that will happen. However, it seems like mandatory information for a Democratic campaign strategist - or any Republican incumbent who won by less than 20 points in 2012.