Nonetheless, it seems clear that Mr. Boehner lacks the confidence of roughly three dozen Republican members of the House, and possibly more. Erick Erickson, of the blog RedState, identified 34 Republicans who he said opposed Mr. Boehner’s bill and another 12 whom he identified as being on the fence.

Say that Mr. Boehner cannot count on the support of 34 of his Republicans when it comes to passing major fiscal policy legislation. That means he would need to identify 18 Democrats who would vote along with the Republicans who remained with him.

Here’s the problem: it might be hard to round up those 18 Democrats.

[T]he once-powerful Blue Dog Caucus, a coalition of moderate Democrats, will have only 14 members in the new Congress…

What that means is that if Mr. Boehner has a significant number of Republican defections, as he did on Thursday night, he will need to win the support of at least some liberal Democrats. And a bill that wins the support of some liberal Democrats will be an even harder sell to Mr. Boehner’s Republicans. For each vote that he picks up from the left, he could risk losing another from his right flank.