(CNN) In the Senate, all roads lead to Joe Manchin.
The West Virginia Democrat and his staff have been engaged for weeks in intensive negotiations with the chairs of key Senate committees ahead of his party's release of a sprawling bill to expand the social safety net, laying down his demands on a wide-range of issues: health care, education, child care and taxes, according to multiple sources familiar with the talks.
And Manchin is making clear he won't cave on aggressive climate provisions sought by many Democrats, throwing a wrench in his party's efforts to make the bill key to combating global warming.
With Democrats needing every vote in their caucus to get the bill through the Senate along straight party lines, Manchin has received more attention than any other Democrat, even as others -- like Arizona Sen. Kyrsten Sinema -- have also balked at the $3.5 trillion price tag. Indeed, as committee chairs have held regular meetings with their members over the summer recess to shape key provisions of legislation under their jurisdiction, they often will later have individual meetings with Manchin, even if he doesn't serve on their respective committees.
As she met with her members on the Senate Health, Education, Labor and Pensions Committee, Washington Sen. Patty Murray, who chairs the panel, also talked privately with Manchin to hear his concerns about provisions on free community college and universal pre-K -- issues that are also central to President Joe Biden's agenda. Her staff has since been in contact with Manchin's aides, while Murray has been in constant communication with other members as well.
Manchin and his staff have been in consistent talks with Senate Finance Chairman Ron Wyden of Oregon, a committee where the two powerful Democrats have clashed over several key provisions central to financing the proposal, including on corporate tax hikes, according to multiple sources familiar with the matter. Wyden has had weekly Zoom meetings with his committee members on individual areas of their proposal, but has made sure to have regular talks with Manchin -- either with him directly or through his staff.
And Manchin has engaged in long discussions with rank-and-file Democrats as well, including Sen. Michael Bennet over the Colorado Democrat's push to broaden and bolster the child tax credit, which the West Virginian wants to bring down to a level far lower than what many in his party want, multiple Democrats said.
On education, Manchin is trying to limit the Democrats' efforts to provide universal pre-K and tuition-free community college. He's talked to Democrats about limiting the number of Americans eligible for pre-K by setting income thresholds, while also discussing ways to measure students' performance for community college assuming their tuition is paid for over two years. And on health care, Manchin has suggested substantially reducing funding for home-care services, a key priority of many Democrats.
The private discussions come amid Manchin's public call last week in a Wall Street Journal op-ed for a "strategic pause" in consideration of the expensive bill, which Democrats are trying to advance through a process known as budget reconciliation since it can be approved along straight party lines in the 50-50 Senate. Democratic leaders want to resolve their disagreements and have a proposal ready by September 15.
"Sen. Manchin's op-ed made clear that both the present and unknown challenges facing our country far outweigh the politics of passing something of this magnitude at this time," a Manchin aide told CNN, referring to the moderate Democrat's concerns over inflation and the ballooning national debt. "This was true last week, and it is today."
The talks underscore the challenges ahead for Senate Majority Leader Chuck Schumer, who needs to win over Manchin but also avoid provoking a revolt among progressives -- particularly in the House -- who are already balking at the West Virginia's private suggestion to bring the price tag of the overall bill down to around $1.5 trillion. And without Senate passage of the reconciliation bill, House progressives are warning they'll derail the Senate's $1.2 trillion infrastructure plan that Manchin was central in negotiating.
"The idea of a $1.5 trillion price tag being sufficient to accomplish those goals for the people is fanciful," Rep. Mondaire Jones, a progressive Democrat from New York, said on CNN.
What remains to be seen is whether the Senate chairs ultimately cater to Manchin's demands or try to railroad him into making a choice: Approve the most sweeping piece of domestic legislation in decades -- or be responsible for sinking it singlehandedly.
"We're moving full steam ahead," Schumer said Wednesday, rejecting Manchin's much-publicized call last week for a "strategic pause" in consideration of the bill.
Schumer and Manchin -- who have long had a frank and collegial relationship -- have been in constant talks throughout the month of August and was not caught off-guard by Manchin's op-ed last week, multiple sources say. Schumer knows full well that he needs to keep his most important swing vote at bay, in addition to Sinema, who has already said she'd oppose a bill that costs $3.5 trillion.
"There are some in my caucus who believe $3.5 trillion is too much. There are some in my caucus who believe it's too little," Schumer said Wednesday. "And we're going to work very hard to have unity because without unity, we're not going to get anything."
To get unity, the committee chairs have been working to ensure that Manchin is not caught off guard by provisions in their plan that they hope to unveil next week.
Helen Hare, a spokeswoman for Murray, said the Washington state Democrat spoke with Manchin and has had "regular conversations" with her committee members since last month. "She's talking to lots of senators with the goal of getting the strongest possible agreement on free community college, child care and all the other policies she's working to get across the finish line," the spokeswoman said.
Some issues may be unresolvable -- such as climate change. Manchin, who represents a major coal-producing state, has balked at Democratic proposals to impose a clean energy standard to significantly reduce carbon dioxide emissions. Democrats have also discussed including a tax on carbon dioxide emissions, something that could lead to industry's use of cleaner-burning fuels.
But Manchin has not been amenable to the aggressive climate targets, leaving it unclear where the talks will land.
"If they're eliminating fossils, and I'm finding out there's a lot of language in places they're eliminating fossils, which is very, very disturbing, because if you're sticking your head in the sand, and saying that fossil (fuel) has to be eliminated in America, and they want to get rid of it, and thinking that's going to clean up the global climate, it won't clean it up all," Manchin told CNN in July of his party's plans. "If anything, it would be worse."