[W]hether the momentum the economy has picked up lately (unemployment was down to its lowest rate since 2008 as of February) stalls, gathers more steam, or is halted will play a big part in how the public perceives the stewardship of the president – and by extension, the Democratic Party. Obama has set his sights on the very lofty goal of winning back the House majority. It’s a long-shot, even under favorable conditions. If the unemployment rate does not continue to drop, it may be near impossible.
Just on this minor point: Why do people continue to predict state elections viewed through national economic numbers? The Democrats' most vulnerable Senate seats are generally in places where unemployment is lower than the national average -- South Dakota (4.4%), Iowa (5.0%), Montana (5.6%), Louisiana (6.0%), Arkansas (7.2%) and West Virginia (7.3%). The exception is North Carolina (9.4%). It's harder to track the trends in congressional districts, but you've got very specific challenges from place to place related to sequestration, and partisan blame for sequestration.
One of the (pretty widely discussed) parodoxes that hurt Mitt Romney's 2012 campaign was this lumpy, regional unemployment map. Some of the bleakest economies, the ones that drove the national number, were in states locked in for Barack Obama -- Illinois, California, New York, New Jersey. Midwestern and Western swing states were recovering more quickly, helping Obama. The advantage for Republicans, next year, is that they get to play where voters are predisposed to vote against Democrats anyway. And so the budget/spending discussion remains pretty remote from the political stakes, which... which doesn't really change anything, does it? No, the effects of Obamacare implementation matter more than this, and are harder to track.