(Darla Cameron / The Washington Post)

This post has been updated with the latest information.

Here's where we stand on Friday: Congress is struggling to pass a short-term spending bill that keeps the lights on for a few more days, which means the government could shut down at midnight.

That's why three out of the four expert observers surveyed by The Fix think a shutdown is more likely than not, or at best 50-50. The House voted largely along party lines and passed a spending bill Thursday night that keeps the government open for a month. Now it goes to the Senate, where there might not be enough votes for it to pass.

And the president is suggesting he might not support anything that comes out of Congress.

“It’s still a very volatile and emotional situation,” Stan Collender, a budget expert and columnist at Forbes, said in an email to The Fix.

“I lean toward a shutdown,” said former Senate GOP budget aide Steve Bell.

“The chances of a shutdown have increased substantially,” said Molly Reynolds, a congressional expert at Brookings Institution.

Here are all the dynamics that lead our budget experts to believe the government will probably shut down the government in the next 17-ish hours.

Senate Democrats oppose the House's short-term spending bill

Senate Minority Leader Charles E. Schumer (D-N.Y.) said on Jan. 17 that "revulsion" toward the GOP's spending bill "was broad and strong," within the Democratic party. (The Washington Post)

Senate Republican leaders are taking a big risk Friday by putting the House's one-month spending extension to a vote. They might not have the votes to pass it.

Republicans will need all of their 50 senators, plus at least 10 Senate Democrats to help them pass a budget, and it looks like they are far short of that. My colleagues on Capitol Hill count some 39 out of 49 Senate Democrats, including nine who voted for a short-term deal last month, as opposed to this bill.

These Senate Democrats have a long list of demands: protecting “dreamers” from deportation, upping opioid treatment spending and natural disaster relief.

“If there are enough Senate Democrats willing to vote against the [short-term spending bill], then I think the odds of a shutdown go up substantially,” Reynolds said.

Senate Republicans may not be able to count on their own, either. Sens. Lindsey O. Graham (S.C.), Jeff Flake (Ariz.) and Rand Paul (Ky.) have all signaled, for varying reasons, that they may vote no.

Maya MacGuineas, president of the bipartisan Committee for a Responsible Federal Budget, spoke to The Fix earlier this week. She thinks lawmakers will work something out, but it will be despite themselves. “I remain positive there will not be a shutdown, but this process sure does beg for a massive overhaul to the budget process, which is in total disarray,” she told The Fix in an email.

The Senate approves a bill to keep the government open for just a few days

If Senate Majority Leader Mitch McConnell (R-Ky.) can't get enough votes for a month-long extension, some lawmakers have signaled they'd be willing to vote on a bill that keeps the government open over the weekend.

But that doesn't solve any of Congress's underlying problems, which is mainly that they can't get a majority of lawmakers to vote for a month-long deal, let alone a year-long spending bill.

And this plan might run into a technical issue, Reynolds points out: The House may not be in session to vote on a weekend spending bill. They were supposed to leave town later Friday. Remember, midnight Friday is the self-imposed deadline for Congress to pass something to keep the lights on.

Trump doesn't know what he wants

(Jabin Botsford/The Washington Post)

The biggest hurdle of all comes after Congress. Any bill that passes Congress still needs to be signed by the president. And even though White House press secretary Sarah Huckabee Sanders said Wednesday that Trump would support a month-long spending bill, by Thursday, the president was suggesting the opposite.

In one mysterious tweet, he ripped away Republicans' strategy to get Democrats on board by saying there shouldn't be funding for the Children's Health Insurance Program funding in this bill.

Ever since then, he's suggested a shutdown was possible and has been blaming Democrats.

“Trump is doing it again,” said Collender, “by saying different things on different days and seriously complicating the outcome by doing so.”

Trump is so unpredictable that his own party has learned not to rely on him to close deals or even agree on deals they come up with. Graham told The Post's Ed O'Keefe on Thursday morning: “We don’t have a reliable partner at the White House to negotiate with.”