Despite being wildly unpopular, Obama would still do better than any Democratic rival who challenged him in the primaries.

That conclusion by Nate Silver jibes with history; ditching an incumbent president leads nowhere:

The evidence, if anything, points in the opposite direction: Mr. Obama is more popular than his policies, and probably gives the Democrats a better chance of maintaining the White House than another Democrat would. Three pieces of data to consider:

First, Mr. Obama's personal favorability ratings - which continue to average about 50 percent - are considerably higher than his approval ratings, which are now around 40 percent. It's not uncommon for favorability ratings to track a point or two ahead of approval ratings - but this is a particularly large gap. Voters remain reasonably sympathetic to Barack Obama, the person, even if they're growing less and less thrilled with his performance.

Can Mr. Obama use that sympathy to persuade hesitant voters to give him another chance? Well, we'll see. But usually when a party would be better off disposing of its incumbent, it's because these numbers run in the opposite direction: the candidate has some personal liability that is overshadowing his policy positions. Textbook examples would include the former Republican Senator Jim Bunning of Kentucky, whose old age (and apparent symptoms of senility) concerned voters, or the retiring Nevada Senator John Ensign, who has been involved in a series of scandals. Mr. Obama, by contrast, is young and healthy and has probably had fewer scandals than any recent president.

The second statistic is Mr. Obama's approval ratings which, although now rather poor, are no worse than you would probably expect from the sour mood of the country. In fact, for most of his first term, the opposite had been true. Based on the precedent established by past presidents, Mr. Obama's approval ratings had been several points higher than they "should" have been based on questions about whether the country was headed in the right direction.

The only realistic alternative at this late date would be Hillary Clinton. And she would have to spend her time criticizing policies she supported publicly, not to mention having to defend Obama's economic record if she were to unhorse him.

The Dems might dream, but they are well and truly stuck with this albatross of a candidate around their neck. They sink or swim with Obama.