Updated at 2:44 p.m.

It's here.

The federal government shutdown that has been mentioned for weeks as a possibility became a reality Tuesday morning after lawmakers failed to strike a deal on a stopgap spending measure.

Senate Democrats and House Republicans have been trading proposals for days that the other side has said are non-starters. Bills that pass one chamber have gained no traction in the other.

Below is an updated breakdown of the proposals that have either (1) been raised and rejected (and may be raised again, perhaps in different contexts) or (2) may be raised down the line as the legislative standoff continues.

We've pulled quotes from Democrats and Republicans that best sum up the prevailing opinion in both parties. We also offer some insight why the proposals matter, and whether or not they can succeed. (Spoiler alert: Almost everything has sparked major disagreement.)

A ‘clean CR’
The Senate has passed a continuing resolution that does not include any of the Obamacare amendments that House Republicans have demanded.

What Democrats say:
Continuing resolutions were always about disputes over money. They were not about political, ideological viewpoints over past legislation.”
Senate Appropriations Chair Barbara Mikulski (D-Md.)

What Republicans say:
I do not see that happening.”
House Speaker John Boehner (R-Ohio)

What to make of it: It's been clear for a while that House Republicans want to use the short-term budget debate to go after Obamacare. Will they ever back down? So far they haven't, even at the 11th hour. And neither have Democrats, who refuse to move from demanding a "clean CR." Democrats have offered to reduce the size of their spending bill, but that's not likely to satisfy conservatives who want the fight over Obamacare to continue. In short, don't count on this option being the one that ends a shutdown -- at least unless and until enough House Republicans move toward it.

A one-week CR
Senate Republicans have been exploring the possibility of passing an even shorter-term CR that would allow time for more debate.

What Democrats say
Look, the bottom line is very simple: you negotiate on this, they will up the ante for the debt limit.”
Sen. Charles E. Schumer (D-N.Y.)

What Republicans say
Despite the Democrats’ refusal to work with the House to solve the problem, Republicans are working to protect the troops, prevent a shutdown and find solutions to the difficulties cause by Senate Democrats’ delays.”
Don Stewart, spokesman for Senate Minority Leader Mitch McConnell (R-Ky.)

What to make of it: Right now, this still looks unlikely. Not only are Senate Democrats against it, but who knows what terms House Republicans would even accept for a short-term deal.

Repealing the medical device tax
The House over the weekend passed a CR that would repeal of the medical device tax and delay Obamacare. The Senate rejected it.

What Democrats say
We can work out something, I believe, on the medical device tax -- that was one of the proposals from the Republicans -- as long as we replace the revenue so that we don't put a hole in our deficit and respond to this in a responsible fashion."
Senate Majority Whip Dick Durbin (D-Ill.)

What Republicans say
And we really should repeal the medical device tax. I mean, 79 senators voted against that thing. That has stopped investment in medical devices."
Sen. Ron Johnson (R-Wis.)

What to make of it: This might just might be the key to resolving things, given that members of both parties have expressed opposition to the tax. But, for it to even be conceivable that Democrats would accept it in a CR, the House would probably have to include it with no other measures that seek to change Obamacare. Can conservatives in the House live with that?

A conference committee
The House GOP proposed early Tuesday that both chambers go to conference.

What Democrats say
We like to resolve issues, but we will not go to conference with a gun to our heads."
Senate Majority Leader Harry Reid (D-Nev.)

What Republicans say
I think it's fair to say none of us want to be in a shutdown, and we're here to say to the Senate Democrats, come and talk to us. This is how we resolve our differences and can work our way out of this kind of situation."
House Majority Leader Eric Cantor (R-Va.)

What to make of it: Senate Democrats are open to a conference committee, but not during a shutdown. So for now, this doesn't look like the way out.

Delaying the individual mandate
House Republican leaders passed a measure Monday that would delay the portion of Obamacare that will require most Americans to have health-care starting in 2014. The Senate rejected it Monday.

What Democrats say
As I have said repeatedly, the Senate will reject any Republican attempt to force changes to the Affordable Care Act through a mandatory government funding bill or the debt ceiling.”

What Republicans say
Families all around the country who are looking at this individual mandate that goes into effect now, starting January 1st, so they have to start buying government-approved insurance or pay a penalty or a tax or a fine, they're saying why is it OK for the president to give businesses an exemption but not give the workers? Why should the boss have an exemption but workers not be exempt from the mandate, for at least a delay of a year?”
Sen. John Barrasso (R-Wyo.), on CNBC

What to make of it: Democrats aren't budging from their refusal to talk about major changes to Obamacare in the context of the budget debate. Since this has already been voted down, it would be hard to imagine that House Republicans bring it up again.

A version of the 'Vitter Amendment'
The second health-care related part of the House GOP's Monday bill was a measure that would strip federal health-care subsidies for lawmakers and their staffs, an idea previously offered by Sen. David Vitter (R-La.).

What Democrats say
Although Sen. Vitter has happily allowed the federal government to pay for part of his health care for years, he wants 16,000 congressional staffers to foot the whole bill.”

What Republicans say
“This bill ensures that all Members of Congress and the White House will finally have to live by the same laws that have been passed, just like all Americans."Republican Study Committee Chairman Steve Scalise (R-La.)

What to make of it: Like the measure to delay the individual mandate, this doesn't seem likely to lead anywhere.

Military pay
The House passed a bill that would keep military personnel paid in the event of a shutdown. The Senate signed off on it, too.

What to make of it: Here's an issue on which Democrats and Republicans are actually aligned. (Yes, these do exist.). It took a worst-case scenario to forge some agreement, but it is an agreement nonetheless.

Cruz's plan B
House Republicans are pushing a plan to break up the spending bills into smaller chunks, an idea first floated by Sen. Ted Cruz (R-Tex.)

What to make of it: This is the latest idea to surface. And if it comes to a vote, it will largely be for political posturing. Why? Because House Republicans will try to pin blame on House Democrats for closing national parks and museums if they object to funding certain areas of the government Republicans will single out.