WASHINGTON — Democrats frantically worked Tuesday to resolve disputes over President Joe Biden's "Build Back Better" proposal, but skepticism persisted that a deal could be reached quickly amid new uncertainty surrounding a potential billionaires tax and new tensions over climate change. "It's just so tenuous. Everything is so tenuous," said Sen. Joe Manchin, D-W.Va., a pivotal centrist who could make or break core components of Biden's sweeping agenda. Manchin has expressed concerns about programs that would guarantee paid leave and extend Medicaid coverage. He did not specify what changes in those provisions would win his support. "Everything is under negotiation," he told reporters. "Everybody's talking constructively. Everybody's trying to work and find that pathway forward." Manchin demurred when he was asked whether his proposed $1.5 trillion spending cap could be increased to secure a deal. "I'm not going to negotiate with you," Manchin told NBC News. The initial price tag for the spending package was $3.5 trillion, but negotiations have made it more likely that the top line will fall below $2 trillion. Manchin has also called for sharply reining in the bill's approach to clean energy. He was accosted Tuesday afternoon outside the Capitol by an environmental activist affiliated with the Sunrise Movement, and some progressive senators are bristling at the thought of adding language that would benefit the fossil fuel industry. "There are provisions that are being considered as part of this package that would be horrific for climate down the road," said Sen. Jeff Merkley, D-Ore., referring to ideas that would "extend the life of methane" and steer the U.S. toward "blue hydrogen." Merkley said lingering issues for the bill as a whole include climate policy, Medicaid coverage gaps, Medicare drug negotiations and an expansion of Medicare to cover dental, vision and hearing benefits. "There's just huge pieces of this that are not nailed down. So each time I hear 'Well, it's almost done,' I don't know what the hell people are talking about," he said. The White House does not expect a significant breakthrough Tuesday, multiple officials said. Biden and his top aides continue to have meetings and calls with lawmakers, officials said, and Biden met with several members of Congress for a closed-door meeting at the White House earlier in the day. The White House is still working through issues like health care, taxes and paid leave, an official said, without offering specifics. An unresolved issue is how to finance the bill after Sen. Kyrsten Sinema, D-Ariz., objected to higher tax rates for wealthy earners and corporations. In recent days Democrats have floated a new revenue raiser that would require billionaires to pay a tax on a "built-in gain" their assets have accrued. Manchin has expressed openness to the idea. But Rep. Richard Neal, D-Mass., chair of the tax-writing Ways and Means Committee, voiced uncertainty, saying his members have yet to review the text or scrutinize the proposal. "We'll have to see what the traffic will bear," he said, a . . . read the full article here.