Senate Democrats and Republicans unveiled on Sunday a roughly $1 trillion proposal to improve the country’s roads, bridges, pipes, ports and Internet connections, setting in motion a long-awaited debate in the chamber to enact one of President Biden’s economic policy priorities.

The package arrives after weeks of haggling among a bipartisan bloc of lawmakers, who muscled through late-night fights and near-collapses to transform their initial blueprint into a roughly 2,700-page piece of legislation. The fate of their labors now rests in the Senate, where proponents of infrastructure reform have little margin for error as they race to adopt the sort of bill that has eluded them for years.

Virtually no part of the U.S. economy is untouched by the plan chiefly put together by Sens. Rob Portman (R-Ohio) and Kyrsten Sinema (D-Ariz.). Roughly half of its $1 trillion overall price tag constitutes new federal spending, with the rest coming from existing, planned investments in the country’s roads, highways and bridges, according to details released in recent days by lawmakers and the White House, which supports the proposal.

Those thoroughfares would see major expansions and repairs under the bill, which has additional investments in the nation’s transit system as well. Senators also said the measure calls for $66 billion targeting passenger railways, which the White House says is the largest such investment since the creation of Amtrak nearly a half-century ago.

Lawmakers plan to set aside $55 billion to improve the country’s drinking water, including a program that seeks to replace every lead pipe in America. There’s an additional $65 billion to expand broadband Internet access nationwide and ensure those who do have connectivity can afford their monthly payments. And Senate lawmakers are pursuing additional sums to upgrade key commercial hubs, including potentially $25 billion for repairs at major airports.

The proposal, called the Infrastructure Investment and Jobs Act, further seeks a significant tranche of funding to combat the threat of climate change, aiming to reduce emissions and respond to the deadly consequences of a fast-warming planet. Lawmakers have called for $73 billion to modernize the nation’s energy grid and $21 billion to respond to environmental concerns, including pollution. And they propose allocating new sums to advance clean-energy technologies, including a $7.5 billion initiative for a first-ever national network of electric vehicle charging stations, they announced last week.

“It takes our aging and outdated infrastructure in this country and modernizes it, and that’s good for everybody,” Portman said in a Sunday night speech, one of many from the deal’s chief architects heralding their work.

Democrats and Republicans say they have covered the full cost of their new spending, one of the thorniest fights among the lawmakers who helped construct the deal. Democrats, led by Biden, initially sought this spring to fund infrastructure investments through tax increases on corporations and wealthy Americans, unwinding the tax cuts that Republicans adopted under President Donald Trump. But GOP lawmakers fiercely rejected the idea, preferring instead to raise some of the money through new fees on those who use infrastructure — an idea Democrats rejected out of a fear that it would hurt average Americans.

Their bipartisan compromise, as a result, omits both new taxes as well as user fees. Instead, it recovers its costs through a pastiche of financing mechanisms, from reclaiming past coronavirus aid funds to collecting unpaid taxes on cryptocurrencies. But there nonetheless remains concern in both parties that some of the math is fuzzy, raising the potential that the package still could add to the federal deficit — and bring about significant fighting on the Senate floor.

With a proposal in hand, that debate began Sunday night under the fast-track timeline laid out by Senate Majority Leader Charles E. Schumer (D-N.Y.). From here, though, Senate leaders hope to finish their work by the end of the week. The chamber then plans to begin work on a second, roughly $3.5 trillion economic package sought by Democrats, underscoring the significant lift awaiting lawmakers in the days before they are set to depart for their planned summer recess.

“I’ve set out two very ambitious goals for the Senate this summer, and we’re now on the way to achieving both,” Schumer said Sunday as he took the necessary procedural step to bring the infrastructure deal to the floor.

Only five days ago did Portman, Sinema and other negotiators announce they had reached a deal, setting in motion a rocky sprint to turn their roughly $1 trillion blueprint into legislative text. The Senate voted overwhelmingly on Wednesday night to start debate on the measure, even before lawmakers had an actual bill in hand, though the chief backers of infrastructure reform saw the development as a positive sign of their political prospects.

“I know it has been difficult, and I know it has been long. And what I’m proud to say is that is what our forefathers intended,” Sinema said.

From here, the bipartisan group of 10 senators faces a delicate task. The lawmakers must keep together their fragile coalition, avoiding the sort of policy disputes that nearly doomed their efforts multiple times since they first announced their ambitions for new public-works spending in June. And they must remain open to changes while not allowing any that could undermine support for the legislation, since any bill ultimately must garner 60 votes in the Senate, where Democrats possess only a razor-thin majority, with Vice President Harris holding the tiebreaking vote.

Sen. Susan Collins (R-Maine), one of the chief negotiators of the infrastructure deal, sounded a note of optimism about the path forward on Sunday. Appearing on CNN’s “State of the Union,” she said it remains “my expectation and my hope” that the $1 trillion proposal could pass the Senate this week.

With every Democrat voting for the deal, the party still would need 10 Republican votes to advance infrastructure investments through the chamber. Collins predicted that those votes ultimately would be there as senators from both parties realize “the very concrete benefits, no pun intended, of this legislation.”

Sen. Joe Manchin III (D-W.Va.), another negotiator, predicted that final passage could come as soon as Thursday — an ambitious timeline that may hinge on lawmakers deftly navigating what might be a difficult amendment process over the days ahead.

Appearing on CNN, Manchin also stressed the bill’s ubiquitous political appeal, calling the new investments “something every state, every area of every state, needs.”

Yet serious political schisms still loom large over the bipartisan measure. Chief among them are concerns about its costs, given lingering doubts that the $1 trillion in new public-works spending is not actually covered by new revenue — and could add to the deficit.

In an early sign of the bickering to come, Sen. Rick Scott (R-Fla.) took his criticisms to the chamber floor on Friday. He lambasted the “lofty and unrealistic revenue estimates” of the package, which he said would result in government spending that increased the risks of inflation.

On Sunday, Sen. Mike Lee (R-Utah) aired his own fiscal concerns. “There are a number of Americans who see all is not well with the way we spend money, the people’s money, within the American government,” he said as he criticized the deal.

Liberal Democrats harbor their own fears about the package: Rep. Alexandria Ocasio-Cortez (N.Y.) told CNN that she had some initial doubts about the financing mechanisms essentially being a boon for corporate America.

Ocasio-Cortez and other House lawmakers previously have questioned the scope of the Senate’s infrastructure investments, believing that Democrats should have sought more as part of the deal, given their narrow but powerful majorities in both chambers of Congress. They have insisted that any new bipartisan deal on public-works spending must move in tandem with the second, roughly $3.5 trillion package, which includes many of Biden’s other economic priorities, including an expansion of federal safety-net programs and other initiatives to fight climate change.

Democrats intend to advance the package on their own — bypassing likely GOP opposition — using a legislative maneuver known as reconciliation that is reserved for budget measures.