Happy Shutdown Eve, America. In a matter of hours one of two things will happen: the Senate and House will come to agreement on a government funding resolution that is signed by President Obama, or they won't, and the government will shut down on Tuesday. Here are all of the details of which to expect — the latter — and why. Update: Follow the last-minute votes and negotiations on our liveblog.

How much time is left before a shutdown?

Hours.

The existing points of contention

The resolution passed by the House on Sunday morning was slightly more subtle than the one it passed about a week earlier. That measure funded the government through December 15, except for programs that are a part of Obamacare. The Senate removed that stipulation from the earlier legislation and moved the funding date to November 15. The House's new offering includes four changes, according to USA Today. First, it moves the date back to December 15. Second, it implements a one-year delay on the implementation of the Affordable Care Act (Obamacare). Third, it repeals a tax on medical devices. And, fourth, it includes what Republicans call a "conscience clause," which delays the requirement that employers include contraception in health coverage.

Both of those latter two points are almost certainly non-starters for Senate Democrats (and Obama). Despite Sen. Joe Manchin of West Virginia last week expressing limited support for a delay in implementing Obamacare, the idea doesn't have enough votes in the Senate to overcome a filibuster, while removing those provisions very much does.

For what it's worth, the medical device tax repeal, long supported by House Majority Leader Eric Cantor, would mean a loss of $29 billion in revenue. Red State's Erick Erickson, a staunch backer of an Obamacare delay, calls the tax repeal "crony capitalism at its worst."

There are additional possible points of negotiation. One is the so-called Vitter amendment, which may be included in the House's response if and when the Senate returns a bill for consideration. That amendment would revise how Congress participates in the Obamacare exchanges, as described by the Washington Post. Or the House and Senate could both approve a short-term measure that gives both sides

The day ahead for Congress

According to Fox News' Chad Pergram, the House will begin work Monday at 10 a.m. The Senate will start work at 2 p.m.

That the Senate only has 10 hours to play with is, as with everything else in this protracted and bizarre fight, a point of contention. On Meet the Press on Sunday, Sen. Ted Cruz of Texas demanded that the Senate return to work that day, instead of being on "vacation." Of course, the timeline is as tight as it is thanks in part to Cruz's obstreperous 21-hour floor speech last week — not to mention his months long crusade favoring conservative obstruction to passing a funding bill in lieu of providing funding to Obamacare.

Senate Majority Leader Harry Reid recognizes that his party is in a position of strength on the issue. The lack of a funding resolution is due entirely to the Republican Party's attempt to relitigate Obamacare, after having failed repeatedly to overturn it legislatively. And, of course, having lost the presidential election. Political Wire dug up a quote from House Speaker John Boehner last November. "It's pretty clear that the President was reelected," Boehner said then. "Obamacare is the law of the land." Reid has held a strong line in opposition to any concession. When Obama wanted to sit down with Congressional leaders to sort out a compromise, Reid nixed the idea. Reid, Politico reports, "believed that it would amount to nothing more than a photo-op that would give the false impression that a serious negotiation was occurring, even warning he wouldn’t attend such a session." As an unnamed top Democrat said to Politico's Mike Allen, "Time to punch the bully in his nose."

Assuming the Senate strips the House's new amendments, conservative groups have pledged to take a hard line themselves. BuzzFeed's Kate Nocera reports on a strategy call held by Tea Party leaders.

"The House needs to completely defund Obamacare, not one penny to Obamacare. If so groups would reluctantly live with a one year no funding deal, but has to fully defund all aspects of Obamacare. Delay without defund or if House funds it in any capacity, then all hell is going to break loose," said a conservative strategist who was on the call.

Whether or not Boehner can — or wants to — corral his conservative caucus will be the key sticking point as a resolution is discussed. So far, he's been unable to do so, as The National Review reports. At that Sunday morning vote, enthusiasm for blocking Obamacare was infectious.

Chants of "Vote! Vote! Vote!" echoed through the room. Standing in the back, Boehner’s deputies watched the scene and smiled. "People went bonkers," says Representative Matt Salmon of Arizona. Representative John Culberson of Texas was so enthused that he yelled, "Let’s roll!" after hearing Boehner’s remarks. Culberson later told reporters he was alluding to the cry of United 93 passenger Todd Beamer.

Polling looks bleak for Republicans

Polls have repeatedly indicated that Republicans will bear the brunt of blowback following a shutdown. A new poll from CNN shows that 46 percent of Americans would blame Republicans, with 36 percent blaming Democrats. 13 percent would blame both. Sixty percent said that avoiding a shutdown was more important than making changes to Obamacare.

The bleakest aspect of that poll for Congress came when respondents were asked their attitudes about both parties.

According to the poll, 58 percent say congressional Democrats are acting like spoiled children, with that number rising to 69 percent for the GOP in Congress. Only one in four say congressional Republicans are acting like responsible adults.

Not even their colleagues in the Senate approve of the House's strategy. On Sunday afternoon, the Republican senator released a statement stating that "the strategy of linking Obamacare with the continuing functioning of government [is] a strategy that cannot possibly work."

What happens if the government shuts down

Our colleagues at The Atlantic spoke with experts on the topic, who offered this assessment.

[T]he vast majority of federal workers will be told to go home next week in the absence of a budget deal. Those who get to stay will come from two groups — one in which federal workers have been explicitly exempted and one in which workers have been deemed to be "essential" through analysis.

While payments to the armed forces might be affected under a normal shutdown, the House passed a bill that the Senate will likely echo permitting such pay to go forward. But most other departments, The New York Times notes, will furlough staff, except things like the FBI and FDA inspectors.

One additional aspect of government that will have funding that is protected as essential? Obamacare. Despite a shutdown, the planned launch of exchange sign-ups on October 1 will continue as scheduled. This has been known since at least July, when Sen. Tom Coburn of Oklahoma asked the Congressional Research Service to explain the effects of a shutdown.

Assuming that no deal is reached by midnight, the next question becomes how long the shutdown would last. Some have predicted that any shutdown would put the economy at risk, making a resolution urgent. Some have argued that a shutdown would be a good thing, giving Congressional Republicans a way to demonstrate their commitment to blocking Obamacare while then letting real negotiations move forward. It's unclear if this will play out in that way, especially given that this is only the first of two major fights coming up this month. On October 17, the government will need to raise the debt ceiling — a much more fraught debate.