(CNN) Sen. Maggie Hassan, a New Hampshire Democrat who is running for a second term next year, has been working behind the scenes to help craft a bipartisan infrastructure deal that could be popular in her swing state.
But she soon will have to make a decision that is bound to be much more divisive: whether to endorse the Democrats' more sweeping $3.5 trillion proposal to expand the social safety net, overhaul immigration laws, grow Medicare and Obamacare, combat climate change and raise corporate taxes to help pay for it.
"I've just been focusing on the bipartisan infrastructure negotiations right now," Hassan said when asked about the massive price tag, sidestepping questions about her party's $3.5 trillion proposal -- just as a number of her more moderate colleagues have done so far.
Senate Majority Leader Chuck Schumer has set a Wednesday deadline to get all 50 members of the Senate Democratic Caucus on board behind their party's plan, which would fulfill much of President Joe Biden's economic agenda. But while liberals are mostly falling in line behind the partisan approach, the caucus's more centrist members have yet to commit, a sign of the land mines facing a Democratic leader who has no margin for error.
West Virginia Sen. Joe Manchin, who has already said he's "very, very disturbed" by the climate provisions in the proposal, was blunt when asked if he would be able to agree to the $3.5 trillion plan by Wednesday.
"That's a challenge," Manchin said.
Every Democratic vote will be necessary for Schumer to pass more than $4 trillion worth of Biden's agenda along two separate tracks. Schumer also set a first procedural vote for Wednesday to take up a smaller, bipartisan plan with roughly $600 billion in new spending focused mainly on "hard" infrastructure -- such as roads, bridges and broadband. Those talks are still ongoing with negotiators struggling with finalizing ways to finance the plan without raising taxes.
At the same time, Schumer has asked all 50 Democrats to give some level of assurance that they'd support moving ahead with a budget resolution that would set the stage for passing the larger $3.5 trillion package this fall.
A Democratic source familiar with the planning said there's a reason for the request: Some of the Senate's progressives are wary of backing the bipartisan deal and will do so only if all 50 members of their caucus agree to the larger, party-line approach. With time ticking before the August recess, and midterm campaigning soon to get into full swing, Schumer needed to amp up pressure to get the bipartisan deal done -- while urging his colleagues to fall in line in an attempt to get both bills to Biden's desk in September.
While Schumer wants total party unity on both approaches, the budget resolution has not yet been written, with only rough outlines released so far, making it hard for some members of the caucus to commit to backing it. The bipartisan talks have not concluded either, with Republicans threatening to revolt against Schumer's deadline if the negotiations aren't finished by Wednesday.
For the bipartisan plan to succeed, they'll need all 50 Democrats to back it -- along with at least 10 Republicans -- to break a filibuster attempt. But the partisan approach is different: It is moving through a budget process -- known on Capitol Hill as reconciliation -- and that requires only a simple majority, meaning it can pass along straight party-lines in the 50-50 Senate.
Yet any Democrat can defect and kill it.
How some of the more moderate members will come down remains a key question.
"I've been focused on a bipartisan compromise," said Sen. Mark Kelly, a freshman from Arizona who faces reelection next year, when asked about the $3.5 trillion plan. "Anything that's going to be proposed I'll have to look at the details of what's in it."
His counterpart from Arizona, Kyrsten Sinema, who is helping lead the bipartisan talks, pointedly refused to answer questions about the $3.5 trillion price tag when asked repeatedly on Thursday.
"I don't even know what you're talking about," Sinema said when asked about Schumer's Wednesday deadline.
Sinema's office told CNN she'll be looking at the details of the reconciliation proposal, rather than any specific top-line dollar amount, to determine if she'll back the measure and consider it good for her state.
Even if Schumer can get support for an initial vote on the budget, that's just the first step.
The budget itself will not include all that much detail on what will actually be a part of the Democrats' own bill, which will head to the floor in September.
Instead the budget resolution sets a top-line spending target for each committee to write its own legislation. That means Democrats would ultimately have to go back and vote again after the final bill is finished, when all the intricate details that can make or break a bill will be included. But they first have to approve the budget resolution, which Schumer wants to pass the Senate before the August recess.
In the lead-up to the announcement of a budget deal earlier in the week, talks had already begun in earnest with moderate Democrats.
Schumer knew his colleagues couldn't be blindsided, and Sen. Mark Warner, a Democrat from Virginia who serves on the Budget Committee and is seen as a close ally to the moderates, took the helm as a leader in helping communicate their point of view in the negotiations. In a nod to more centrist members, Democrats are vowing that their plan will be fully paid for, an assurance that helped win the backing of the 11 Democratic members of the committee whose views span the ideological spectrum of the caucus.
Yet despite a series of informal discussions, an aide familiar with the matter tells CNN, moderate Democrats never promised they'd back the committee's proposal. They did make it clear they would not back the initial proposal from Senate Budget Chairman Bernie Sanders that totaled a whopping $6 trillion, a major reason why that number was pulled back.
The uncertainty on the budget comes as Democrats are just weeks from their scheduled August recess.
When lawmakers return in September, they'll be confronted with a spending deadline and a looming need to increase the debt ceiling. The efforts will also be bumping up against the unofficial start of the 2022 midterm election cycle, which may make it harder for members on the ballot to vote for tax increases even if they would affect only those who make more than $400,000 a year.
Montana Sen. Jon Tester, who referred to the $3.5 trillion as a "s--- pile of dough" earlier this week, suggested he's open to the price tag but needs to look at the details more closely. But the moderate Democrat didn't seem too concerned about the pressure Schumer is placing on his members.
"I think he's pushing," Tester said. "I think it's good."
This story has been updated with additional developments Friday.