To get around Republican obstruction, Democrats are using a fast-track process known as reconciliation that shields legislation from a filibuster. That would allow it to pass the 50-50 Senate on a simple majority vote, with Vice President Kamala Harris casting a tiebreaking vote.
But it would still require the support of every Democratic senator — and nearly every one of their members in the House. Democratic leaders and White House officials have been haggling behind the scenes to nail down an agreement that could satisfy both Mr. Manchin and Ms. Sinema, who have been reluctant to publicly detail which proposals they want to see scaled back or jettisoned.
Congressional leaders aim to finish their negotiations in time to act on the reconciliation bill by the end of October, when they also hope to move forward on another of Mr. Biden’s top priorities, a $1 trillion bipartisan infrastructure bill that would be the largest investment in roads, bridges, broadband and other physical public works in more than a decade.
“As with any bill of such historic proportions, not every member will get everything he or she wants,” Senator Chuck Schumer of New York, the majority leader, wrote to Democrats in a letter ahead of the chamber’s return on Monday. “I deeply appreciate the sacrifices made by each and every one of you.”
It remains unclear which sacrifices will have to be made, with lawmakers still at odds over the best strategy for paring down the plan, let alone how to structure specific programs. The most potent plan to replace coal and gas-fired plants with wind, nuclear and solar energy, for example, is likely to be dropped because of Mr. Manchin’s opposition, but White House and congressional staff are cobbling together alternatives to cut emissions that could be added to the plan.
Liberals remain insistent that the bill — initially conceived as a cradle-to-grave social safety net overhaul on par with the Great Society of the 1960s — include as many programs as possible, while more moderate lawmakers have called for large investments in just a few key initiatives.
In the midst of the impasse, rank-and-file lawmakers have been left to return home to their constituents to try to promote a still-unfinished product that is shrouded in the mystery of private negotiations, all while explaining why a Democratic-controlled government has yet to deliver on promises they campaigned on.