Here’s something to add to the fact that Obama isn’t doing Democratic candidates any favors with his endorsement, from National Journal (emphasis added):
The advice from Democratic consultants and strategists is almost unanimous: Run away from the president, and fast. A prominent Democratic pollster is circulating a survey that shows George W. Bush is 6 points more popular than President Obama in “Frontline” districts — seats held by Democrats that the Democratic Congressional Campaign Committee sees as most vulnerable to Republican takeover. That Bush is more popular than Obama in Democratic-held seats is cause for outright fear.
And:
“He is a walking radioactive disaster,” one senior Democratic operative said of the president.



