Princeton economists: democratic presidents are just "lucky"

Screen Shot 2014-08-13 at 10.19.04 AMIt's well established that the US economy fares better when a democrat is president. Why is this?

A study by economists at Princeton attributes it to luck. "There is no other causal explanation." I'm not a Princeton economist and I haven't done a study, but I think there's more that luck involved.

The lucky left