Will the Senate just go along and pass the bill?

It's almost out of the question. Even before the House voted, Senate Majority Leader Harry Reid rejected their bill as "pointless." “We continue to be willing to debate these issues in a calm and rational atmosphere," the Nevada Democrat said. "But the American people will not be extorted by Tea Party anarchists.” The chances of Democrats accepting the one-year delay are basically zero. Shutdown or no, the insurance exchanges central to the law are kicking in this week, meaning a delay would be a logistical nightmare. And Democrats see the delay as simply the setup for later repeal efforts -- not unreasonably: Republicans have (1) worried publicly that once the law is in place, it will be impossible to repeal, giving Democrats an incentive to resist any slowdown; and (2) described delay as prelude to elimination, as Mitt Romney did in an interview with CNN on Friday.

What about the medical-device tax, though?

Some Republicans hope Reid would accept a deal that eliminated the delay but accepted the repeal of the medical-device tax. That would avoid seriously undermining the health-care law, but allow Republicans to save face with the conservative base (at least theoretically). Yet Democrats have remained unified and shown little appetite for eliminating the tax, which would produce an estimated $29 billion in revenue over 10 years. Of course, even if the Senate did pass both measures, President Obama has vowed to veto them, so it's largely irrelevant.

If this is doomed to fail, why did Republicans do it?

House GOP leaders have decided they'd rather gamble on the uncertain political blowback from a shutdown than incur the certain wrath of conservatives in their caucus and base by backing down. While Speaker John Boehner has said repeatedly that neither he nor the American people want a shutdown, he's given in to conservative hardliners in his caucus. Majority Leader Eric Cantor made that choice explicit: “We’ve had enough of the disunity in our party .... The headlines are Republicans fighting Republicans. This will unite us. This protects the people who sent us here from Obamacare.” Yet it's not clear even this will placate the far right. Writing on the popular conservative site RedState, Daniel Horowitz blasted the bill the House passed Sunday as weak tea.

What happens now?

The Senate was gone for the weekend, but will reconvene Monday and take up the House bill -- but that isn't scheduled until 2 p.m., when there are 10 hours left to shutdown. Barring an unforeseen deal or a major blink from the Democrats, the Senate will table the tax repeal and the delay and send the funding resolution back to the House -- in other words, the exact same language the Senate sent the House on Friday. Unless House conservatives blink, or unless Boehner is willing to pass this so-called "clean CR" with Democratic support, the government will close.