The thrill tingling up the leg of Chris Matthews has become something else trickling down his leg. Democrats are worried that they will lose the White House in 2012 — and both chambers of Congress by bigger margins than the Republicans have enjoyed since Hoover. In a piece at Salon magazine, Matt Stoller, a fellow at the Roosevelt Institute, openly asks about getting some challengers to President Obama in next year’s primaries. Noting that Obama’s approval dropped below 40% in the Gallup, Stoller wrote, “George W. Bush’s approval rating didn’t drop this low until Katrina hit.” That was in 2005,...