Now correlation is not causation, but the best explanation for last summer's serious dip in the economic recovery?  The Republican-induced debt ceiling "negotiation" (i.e., hostage-taking of the American economy).  Check out these graphs from a nice Bloomberg piece from economists Betsey Stevenson and Justin Wolfers:

Of course, now they are threatening to do this again.  Here's Stevenson and Wolfers:

In other words, congressional Republicans are taking the government’s creditworthiness hostage when they threaten not to increase the debt ceiling.