Democrats’ Climate Deal Isn’t Done Yet. Here Are the Remaining Hurdles.

WASHINGTON — When Senator Joe Manchin III of West Virginia, a key centrist holdout, announced a surprise deal last week with Chuck Schumer of New York, the majority leader, on a climate, energy and tax package, Democrats exulted that a significant piece of their domestic policy agenda had been saved.

But the agreement is anything but a done deal.

Now Democrats are racing to muscle the package — packed with hundreds of billions of dollars in climate and energy proposals, a major drug price reduction initiative, tax increases and health care subsidies — through the evenly divided Senate over united Republican opposition. They are doing so under a process known as budget reconciliation, which allows certain tax and spending bills to move quickly and avoid a filibuster but also is subject to strict rules that limit what can be included.

“Our timeline has not changed, and I expect to bring this legislation to the Senate floor to begin voting this week,” Mr. Schumer said on Monday, speaking on the Senate floor.

Here are the hurdles that remain before President Biden can sign the package into law.

Senator Kyrsten Sinema needs to sign off.

With Republicans unanimously opposed, Democratic leaders need all 50 members of their caucus to remain united behind the legislation.

At least one centrist, Senator Kyrsten Sinema of Arizona, has not said whether she plans to support the legislation, which contains at least one proposal that she has previously opposed: narrowing the so-called carried interest loophole, which allows private equity executives and some wealthy hedge fund managers to avoid the higher tax rates that entry-level employees pay.

A spokeswoman has said that Ms. Sinema continues to review the measure and await guidance from the Senate parliamentarian. Mr. Manchin said he expected to speak with Ms. Sinema on the Senate floor on Monday evening, as senators returned to Washington for votes.

“I haven’t had any conversations with anybody during the process because I wasn’t ever sure that we would get to a finale, to get a completed bill,” he said. Mr. Manchin added that he considered Ms. Sinema a friend and that she had a substantial role in shaping the deal, including in hammering out the prescription drug pricing piece and in scaling back the tax increases.

The bill must be blessed by the Senate’s umpire.

By using reconciliation, Democrats can bypass Republicans entirely, but they also must adhere to strict budgetary rules that restrict its scope and structure. One major condition, named the Byrd Rule after its architect, former Senator Robert Byrd of West Virginia, includes a ban against any provision that does not directly change revenue or spending.

The arbiter of the rules is the Senate parliamentarian, Elizabeth MacDonough. Along with staff, Ms. MacDonough is scrubbing and analyzing the pieces of the package to determine whether they adhere to the rules, in a process affectionately known on Capitol Hill as a “Byrd bath.” Republicans, who are seeking to derail the legislation, also plan to challenge key elements of the measures as violations of the Byrd Rule.

Democrats have labored for months over the details and expressed confidence that they would be able to preserve its central elements.

“We’re very careful about that,” Mr. Manchin said on Monday, speaking to reporters on Capitol Hill. He added, “There’s an awful lot of good stuff in this bill.”

Mr. Schumer, speaking at a news conference last week, suggested that Democrats might also incorporate additional changes, including a proposal aimed at lowering the price of insulin.

Senators must endure a ‘vote-a-rama.’

Before voting on final passage, senators will have to sit through 20 hours of debate, evenly divided between both parties, unless they agree to skip some of the time. It is also possible that a Republican will force Senate clerks to read the entirety of the 725-page bill aloud, as a way of objecting to the process, as they did before passage of the $1.9 trillion pandemic aid law last year.

But for Democrats, the biggest hurdle comes after the debate, when the Senate will launch into a rapid-fire series of amendment votes known as a vote-a-rama. That is when the rules allow any senator to offer any proposal with no time limit, usually yielding an hourslong series of politically fraught votes that are designed to sap support for the legislation or put its proponents in a tough spot — or both.

In anticipation of some immigration-related amendments, Senator Bob Menendez, Democrat of New Jersey, called on his colleagues to “defend immigrant communities against the GOP’s plans to use reconciliation to divide us and to advance Trump’s hateful and destructive policies towards immigrants.”

Mr. Manchin, pressed by reporters on Monday, did not explicitly say whether he had committed to voting against any Republican amendments.

“We have a good, balanced piece of legislation. It’s taken me eight months to get here,” Mr. Manchin said. “The process is what it is. You respect the process, and we’ll see what happens.”

In a notice reviewed by The New York Times, Democratic floor staff offered some advance advice for senators and their aides as they looked toward the marathon voting session. “Please be patient, stay hydrated, wear comfortable shoes, bring snacks for your hideaway, a blanket for your lap as it usually gets cold in the chamber at night and anything else to make you comfortable as we hunker down and get to work,” it said.

Democrats need to stay coronavirus-free.

Unlike the House, the Senate does not have proxy voting that enables lawmakers to vote remotely. The even partisan split in the chamber means that, if all Republicans were present, all 50 senators who caucus with Democrats would also have to be present to muster enough votes for the measure, which would still need the tiebreaking vote of Vice President Kamala Harris to pass.

A recent uptick in coronavirus cases in Congress could imperil those plans.

Senator Richard J. Durbin of Illinois, the No. 2 Democrat, remained in quarantine on Monday after testing positive last week, but he was expected to return before the end of the week. One Republican, Senator John Cornyn of Texas, said on Monday that he had tested positive for the coronavirus, but said of a vote on the reconciliation bill, “If it happens, I will be there, consistent with CDC guidelines.”

The House needs to pass the package.

Assuming the legislation clears the Senate, the House will need to return to Washington to approve the measure. While lawmakers remain scattered across the country for a scheduled summer recess, Speaker Nancy Pelosi of California and Democratic leaders have said they will call the chamber back into session — with 24 hours’ notice — to vote on the plan.

With just a few votes to spare in the House, Democrats will have to remain united behind the plan to push it through over Republican opposition. Some progressives have expressed frustration about the scaled-down scope of the package and fossil fuel provisions included at the insistence of Mr. Manchin. But many of them have praised the ambitious climate initiatives as worthy of support.