Against these bullish historical trends are set two very bearish ones. The first is that no president since FDR has run for reelection with the unemployment rate above 8 percent. And the outlook for 2012 is grim. The White House Office of Management and Budget projects 8.1 percent unemployment in 2012. So does the Congressional Budget Office. And those are the rosy scenarios. Other forecasters, from Goldman Sachs to the IMF, predict that the unemployment rate will be 10 percent in 2011 and only somewhat lower in 2012…

The final trend, however, is the most troubling for Obama, because it hints at an underlying problem with his presidency: Since FDR, no president has won reelection without enlarging his share of the popular vote…

These numbers suggest that an essential feature of successful presidents is that they find ways to broaden their coalitions. Doing the opposite—pursuing policies which shed support, but keep just enough of it to maintain a majority—is a very difficult needle to thread. How difficult? FDR in 1940 was the first president to do it since Andrew Jackson in 1832. And he had the Great Depression and World War II working in his favor and was starting from the second-highest popular-vote margin ever recorded.