The problem is that it’s not clear what Mr. Obama can do about this prospect. Conventional wisdom in Washington seems to have congealed around the view that budget deficits preclude any further fiscal stimulus — a view that’s all wrong on the economics, but that doesn’t seem to matter. Meanwhile, the Democratic base, so energized last year, has lost much of its passion, at least partly because the administration’s soft-touch approach to Wall Street has seemed to many like a betrayal of their ideals.

The president, then, having failed to exploit his early opportunities, is pinned down in his too-small beachhead.

If the Democrats lose badly in the midterms, the talking heads will say that Mr. Obama tried to do too much, this is a center-right nation, and so on. But the truth is that Mr. Obama put his agenda at risk by doing too little. The fateful decision, early this year, to go for economic half-measures may haunt Democrats for years to come.