WASHINGTON (AP) — It's Washington's enduring question: What does Joe Manchin want?

But increasingly the answer is crystal clear. The conservative West Virginia Democrat wants to dismantle President Joe Biden's proposed climate change strategies and social services expansion in ways that are simply unacceptable for most in his party.

So the question becomes less about what Manchin wants and more about whether Biden can bring him, the party's other centrist senators and its progressives to middle ground and salvage his once-sweeping $3.5 trillion proposal from collapse.

As the White House pushes its Democratic allies on Capitol Hill to wrap up slogging negotiations before end-of-the-month deadlines, pressure is mounting on the party to hold its slim majority in Congress together to deliver on Biden's priorities. The president will meet with House lawmakers from both groups again Tuesday at the White House. Biden spoke by phone with Manchin on Monday, and Manchin met separately with two progressive leaders: Sen. Bernie Sanders of Vermont and Rep. Pramila Jayapal of Washington state.

"We are at a point where we feel an urgency to move things forward," Biden press secretary Jen Psaki acknowledged Monday.

For months, Manchin has publicly and repeatedly balked at the size and scale of Biden's plan to expand the social safety net, tackle climate change and confront income inequality.

Already, he and fellow centrists, including Democratic Sen. Kyrsten Sinema of Arizona, have forced Biden to concede that the final price tag will likely be much smaller, likely around $2 trillion — largely paid for with higher taxes on corporations and the wealthy, those earning more than $400,000 per year.

But as negotiators sift through the details of what's in and out of the proposal, it's Manchin's priorities that are driving much of the debate, infuriating colleagues and complicating a deal.

To start, Manchin is on board with raising the corporate tax rate to 25%, though not quite as much as the 26.5% Democrats have proposed, to finance Biden's expansive vision, agreeing that corporations should pay their "fair share" at a time when many have reported paying zero taxes.

But after that, the coal-state senator parts ways with progressives and most others in his party.

By insisting on a "fuel neutral" approach to energy policies, he threatens to wreck a cornerstone of the climate change plan, the Clean Energy Payment Program, which would offer grants to power companies that increase clean energy generation by 4% each year and fine those that do not.

On another major issue, by interjecting work requirements or income thresholds for government aid recipients he wants to limit new child care and health care programs to the neediest Americans.

With a striking ability to saunter into the spotlight with wide-ranging demands, Manchin is testing the patience of his colleagues who see a once-in-a-generation opportunity to reshape government programs slipping away to his personal preferences. With Republicans fully opposed to Biden's plans, the president needs all Democrats in the 50-50 split Senate for passage.

"I would hope that we're going to see some real action within the next week or so," said Sanders, the Vermont Independent, after meeting privately with Manchin.

"We discussed the way forward," Sanders said.

As chairman of the Senate Energy and Natural Resources Committee, Manchin says he has been forthcoming both publicly and privately about his concern that some Democratic proposals may be detrimental to his coal and gas-producing state.

In conversations with the White House over the weekend, Manchin reiterated his opposition to the clean energy plan — this as Biden prepares to head to the U.N. Climate Summit at the end of the month and climate envoy John Kerry warns against failure as the administration seeks to regain leadership on the climate issue.

Under Biden's proposal in the emerging bill, the U.S. would provide financial rewards to electric utilities that meet clean energy benchmarks and impose financial penalties on utilities that don't, in line with the president's goal of achieving 80% "clean electricity" by 2030.

While the Democratic plan focuses on renewable energy sources such as wind and solar power, Manchin insists the tax breaks received by fossil fuels should be preserved, along with breaks for wind and solar. He also says natural gas "has to be" part of the mix.

Natural gas produces fewer carbon emissions than coal or oil but has overtaken coal as the largest source of carbon pollution in the U.S. power sector, thanks in part to the U.S. fracking boom.

"I am all for clean energy, but I am also for producing the amount of energy that we need to make sure that we have reliability," Manchin said.

Progressives have pushed back hard.

"No climate, no deal," said Sen. Ed Markey, D-Mass., at a recent Capitol news conference.

"And let me be clear: natural gas is not clean energy and it is not climate action," he added.

Lawmakers are now considering a "menu" of other emission reduction options to replace Biden's clean energy plan. Manchin has pushed for "carbon capture" technology that would allow coal and natural gas to be burned while trapping harmful emissions, but he laments it's "so darn expensive that it makes it almost improbable to do."

A middle ground could emerge in a proposal from Sen. Ron Wyden, D-Ore., the chairman of the Finance Committee, who has said the bulk of greenhouse gas emission cuts would come from an energy tax overhaul he is spearheading.

Among tax changes his committee is considering are tax credits for energy producers that reduce emissions, and pollution fees to be paid by industries for every ton of planet-warming carbon dioxide they emit.

A carbon tax is seen by economists as the most effective way to cut fossil fuel emissions, and the American Petroleum Institute, the chief lobbying arm of the oil and gas industry, has endorsed the idea of a price on carbon emissions.

While Manchin's climate-related objections are central to the debate, he is also pushing Democrats in other ways, by limiting the expanded social services to only people of modest or lower income levels.

Already, some of Biden's proposals including a child tax credit, come with income thresholds, in keeping with the president's interest in targeting the help to middle class Americans. Other help, including the proposed expansion of Medicare to include dental, vision and hearing aid benefits, would be available to all seniors, regardless of income level.

The White House acknowledges there could be some income limits imposed.

"We're talking about targeting and focusing the president's proposals in some areas on people who need help the most," Psaki said.