Still, a primary challenge, even if waged by a less-significant contestant, is a serious matter. Every president who lost re-election in the last half century has first been weakened by a primary fight—Gerald Ford, Jimmy Carter and George H.W. Bush being cases in point. Many of the three million voters Pat Buchanan attracted in 1992 against Mr. Bush, for example, wound up voting for Ross Perot in November. This allowed Bill Clinton to win with just 43% of the popular vote…

Key donors have told the White House that the president should decide for certain whether he’s running for re-election by the end of December. Should Mr. Obama’s approval ratings slip further next year, there’s talk that some donors may call on him not to run, or promote an independent candidacy by New York Mayor Michael Bloomberg…

Most liberals I spoke to don’t support a primary challenge. Jane Hamsher, founder of Firedoglake.com, a leading liberal blog, is less categorical. She blames Mr. Obama for “appropriating the progressive message, and then not governing as one.” She has always backed “a diversity of voices in the primary process as a sign of a healthy democracy.”