Just a few weeks ago, the idea of Democrats actually shutting down the government over the Deferred Action for Childhood Arrivals program seemed like a proposition that only the caucus’s liberal members would support.

Fast-forward to Friday, the next deadline on a spending bill to fund the government. With House Republicans proposing yet another short-term spending bill with no immigration solution attached, Democratic leadership and rank-and-file members in the Senate are getting fed up. And now even moderate Democrats who had previously voted to pass short-term spending bills are looking like they won’t go for one to keep the government open.

Case in point: Sen. Jon Tester (D-MT), considered one of the more vulnerable red-state Democrats up for reelection in 2018 and a reliable vote for past short-term spending bills.

“I think it’s a bad proposal, I’ll just tell you that, and it has nothing to do with DACA; it’s a bad proposal,” Tester said of the latest continuing resolution (CR) on Wednesday. “It doesn’t push us in the direction we need to go.”

When asked if he would vote “no,” Tester responded, “What does it sound like?”

In the past, Republicans could cobble together enough Democratic votes from senators in conservative or swing states including Sens. Joe Donnelly (IN), Heidi Heitkamp (ND), Joe Manchin (WV), Claire McCaskill (MO), Bill Nelson (FL), Debbie Stabenow (MI), and Tester. But the political appetite among these Democrats to pass another short-term spending bill is looking less sure.

“The overwhelming number in our caucus have said they don’t like this deal and they believe if we kick the can down the road this time, we’ll be back where we started from next time,” Senate Minority Leader Chuck Schumer said during a Wednesday press conference. He described the Democratic sentiment toward the proposed short-term CR with one word: “revulsion.”

Heitkamp sounded similarly frustrated as she left Senate votes on Wednesday afternoon.

“I do not think this is a way to legislate,” she said. “Why is that we’re told, ‘Just give us this extra time and we’ll get the job done by the middle of next month,’ and it doesn’t happen? There’s a level of embarrassment about the ability of the United States Congress to do its job. We’re signaling defeat once again with the CR.”

On Thursday morning, Virginia Sens. Tim Kaine and Mark Warner, both Democrats, announced they wouldn’t support a short-term spending bill.

“Congress should remain in session with no recess until we work out a long-term bipartisan budget deal that addresses all issues,” Kaine said in a statement. He added that while he would be open to funding the government for a few days to work out final negotiations, continuing to punt a spending bill was not palatable.

“The Republican leadership has to get serious about finding a budget deal and quit relying on short-term patches,” he said.

The shutdown math

The last short-term spending bill sailed through the Senate chamber on a 66-32 vote when it last came up in late December. Its path through the Senate on Friday is looking much narrower; by Thursday afternoon, senior Democratic aides said Democrats were confident they had enough votes to block a spending bill.

JUST IN: Democrats have enough votes to block the spending bill in the Senate and prevent Republicans from keeping the government up and running, senior Democratic aide tells @NBCNews — NBC Politics (@NBCPolitics) January 18, 2018

Let’s break down the shutdown math.

The magic number to pass a spending bill in the Senate is 60 votes. Republicans have a slim majority, but they need Democratic votes in order to pass the spending bill and keep the government open. With Sen. John McCain (R-AZ) still out of the Senate for health reasons and an Alabama Senate seat recently flipping from red to blue, Republicans need nine Democratic votes to pass the spending bill (or CR).

Each time a short-term spending bill has come up, more Democrats have voted against it. For instance, just eight Democratic senators voted against a CR on December 7. That number increased the next time it came up for vote on December 22, when a total of 29 Democratic senators, plus Sen. Bernie Sanders (I-VT), voted against it.

In late December, 17 Democratic senators voted to pass the spending bill. They can be broken down easily into two groups: those who are up for tough reelections in red states in the 2018 midterms, and those who are electorally safer.

It’s not just some red-state Senate Democrats; others in safer seats who voted for past continuing resolutions said they wouldn’t vote for this one, including Sens. Jeanne Shaheen (NH), Tom Carper (DE), Tom Udall (NM), and Martin Heinrich (NM). Maine Independent Sen. Angus King is reportedly leaning “no” because he’s frustrated with the lack of a long-term spending plan.

And Republicans can’t be assured their caucus will all vote in line; Sens. Mike Lee (R-UT) and Rand Paul (R-KY) have voted against previous short-term funding bills. Graham and Sen. Mike Rounds (R-SD) added their names to the list of “no” votes on Wednesday, saying they were fed up with the stalling from the Trump White House.

“We don’t have a reliable partner at the White House to negotiate with,” Graham told reporters as he walked into the Capitol Thursday morning. “This has turned into an s-show for no good reason, and the only way out of this thing is to grow up a little bit — and I think that’s going to happen.”

But at least one red-state Democrat is holding firm and voting for a CR on Friday; as reporters surrounded West Virginia’s Joe Manchin on Wednesday, he had one thing to say.

“I want to keep the government open.”

So far, it’s unclear whether enough of Manchin’s colleagues will join him to pass another short-term bill.

Activists are calling on Democrats to stand on principle

Throughout the past short-term spending deals, some Democrats have been nervous about the political implications of a shutdown getting pinned on their party, especially with the 2018 midterms a little more than eight months away.

Democrats were hesitant to pull the trigger on a shutdown in past months. But with a bipartisan deal on the table and the Trump White House and House Republicans standing in the way, Democrats have more ground to stand on when they say they have tried to negotiate in good faith but haven’t been able to get key Republicans to cooperate.

And there’s heavy pressure to stand firm from immigrants, activist groups, and mainstream Democrats.

“Standing on principle is good politics,” said Ben Wikler, Washington director of MoveOn.org.

MoveOn recently commissioned a poll of voters in swing states including Florida, Indiana, Missouri, Montana, North Dakota, Ohio, Pennsylvania, Virginia, and West Virginia, and found that by an 11-point margin, voters believed Republicans would be responsible for a shutdown if one were to happen.

There is also widespread support for a long-term DACA fix in the American public, including from Republicans. Many immigrants’ rights groups are closely aligned with the progressive grassroots movement.

And immigrants have been waiting for a fix for nearly two decades. They’ve been asked to swallow a lot of compromises over the years, and Democrats’ failure to secure permanent protections for undocumented youth who have spent nearly their whole lives in the United States is unacceptable to many.

“Every time Democrats vote for a CR, it makes them look weaker,” said Angel Padilla, policy director for Indivisible, a national activist group that has been very vocal on immigration. “These are tough votes, but people are fighting for their lives and fighting for their rights.”

It’s not just activist groups telling Senate Democrats to hold the line during Friday’s vote. The Center for American Progress Action Fund recently released a memo on behalf of its president, Jennifer Palmieri, formerly a key Obama White House and Clinton campaign staffer, echoing the same message. In the memo, Palmieri issued a call to congressional Democrats to stand strong for DREAMers or face the consequences.

“If Democrats can’t even stand up to Trump and Republicans in defense of Dreamers —whose moral case is unassailable — they will leave a lot of progressives wondering who Democrats will fight for,” Palmieri wrote. “At that point, Latinos may not be the only constituency within the Democratic base that becomes dispirited and disengaged. If Democrats don’t try to do everything in their power to defend Dreamers, that will jeopardize Democrats’ electoral chances in 2018 and beyond.”