James Fallows says there are two basic facts required for every government shutdown story. First, if House Speaker John Boehner proposed a "clean" budget bill that didn't try to defund Obamacare, it would pass today by a wide margin in the House, as it has already passed in the Senate, because all Democrats and enough Republicans would vote for it. Second, Boehner won't do it.
A reasonable follow-up question is: Why not?
Robert Costa, a reporter with National Review, tells Ezra Klein (emphasis added):
There are 30 to 40 true hardliners [in the House demanding that government funding be tied to Obamacare's defunding]. But there’s another group of maybe 50 to 60 members who are very much pressured by the hardliners. So he may have the votes on paper. But he'd create chaos. It'd be like fiscal cliff level chaos. You could make the argument that if he brought a clean CR to the floor he might have 100-plus with him on the idea. But could they stand firm when pressured by the 30 or 40 hardliners and the outside groups?
So, by one close observer's count, less than 10 percent of the House of Representatives is preventing the government from opening unless the White House defunds its signature legislation. Not a 51-percent majority. Not a 41-percent "filibuster majority." A 10-percent "bully majority" that has prevailed upon another 10 to 15 percent of the House. Meanwhile the shutdown is already endangering assistance to low-income families, preventing cancer patients from participating in NIH clinics, and shutting down Head Start programs.