All presidents have to compromise. Successful ones, like Reagan and Mr. Clinton, manage to do so while assuaging the objections of their base. So far Mr. Obama has proved incapable of doing both at once. Of late, however, the president has been acting like a primary candidate. His angry speech to Congress two weeks ago and the tax hike he proposed this week have drawn progressive plaudits. Mr. Obama’s newly confrontational attitude toward the GOP may be sufficient to reinspirit the left and forestall any primary protest. In that case, Messrs. Nader and West have simply found a parade and gotten in front of it.

The question for the president then will be whether he can win back the center. His best shot may be to run a viciously negative campaign against the Republican nominee. That would suit Messrs. Nader and West just fine. Their letter asserts that their protest candidates would “display a sobering contrast with the alarmingly weak, hysterical, and untested field taking shape on the right.” It doesn’t occur to them that the extremity of their own ideology may repel the voters who will decide the election. It didn’t occur to Pat Buchanan either.