Focusing on the Economy a losing strategy

I was watching Benjamin Shapiro on C-Span this weekend. He told me something that just floored me. A bad economy works in favor of Democrats not Republicans. FDR won 3 consecutive terms in the worst economy in history. In a bad economy Republicans are seen as taking away the safety net. Shapiro also noted that Reagan beat Carter on calling him out on absolutely everything the biggest being foreign policy. By ignoring gay marriage and abortion and not fighting back on the social issues, Ken Cuccinelli is allowing Terry McAuliffe to define him. Just concentrating on the economy has proven to be a losing strategy ie Mitt Romney. How else can you explain Obama winning a second term in one of the worst economies in 30 years?