Senate negotiators will return to work on Sunday after failing to reach a bipartisan agreement “in principle” Saturday evening on a massive stimulus package, despite reporting significant areas of consensus.

Lawmakers had hoped to finalize a deal on Saturday evening after missing a deadline Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellOcasio-Cortez to voters: Tell McConnell 'he is playing with fire' with Ginsburg's seat McConnell locks down key GOP votes in Supreme Court fight Video shows NYC subway station renamed after Ruth Bader Ginsburg MORE (R-Ky.) had set for the end of the day Friday.

Instead, negotiators will work to resolve disagreements in several areas ahead of a key procedural vote scheduled for 3 p.m. Sunday.

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"You're not going to have a product that's signed off by everybody tonight because there's still a couple of outstanding issues, but it will include a lot of Democratic ideas. So in that sense, it will reflect a Democrat and Republican approach," said Sen. Rob Portman Robert (Rob) Jones PortmanMcConnell locks down key GOP votes in Supreme Court fight Romney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery MORE (R-Ohio).

Senate Minority Leader Charles Schumer Chuck SchumerRepublican senator says plans to confirm justice before election 'completely consistent with the precedent' Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Graham signals support for confirming a Supreme Court nominee this year MORE (D-N.Y.) said he was “optimistic” there would be a deal but added that “we're going to continue working through the night.”

A spokesman for Schumer, however, disputed GOP claims that the emerging Senate bill represents a bipartisan compromise.

“Democrats very much want to reach a bipartisan agreement to address this major health and economic crisis. There is not yet an agreement, and we still have not seen large parts of the Republican draft,” said the Schumer aide.

Congress’s top leaders, the so-called four corners, will meet at 11 a.m. Sunday to negotiate the legislation. It will be the first time Speaker Nancy Pelosi Nancy PelosiAs families deal with coronavirus, new federal dollars should follow the student Sunday shows - Ruth Bader Ginsburg's death dominates Hypocrisy rules on both sides over replacing Justice Ginsburg MORE (D-Calif.) will sit down with McConnell to discuss the $1 trillion-plus package.

Senators and the White House appear to have reached tentative agreements on key points such as a plan to distribute $1,000 in direct tax rebates, a $250 billion expansion of unemployment insurance, a payroll tax holiday for small businesses, and the Office of Management and Budget’s request for $46 billion in emergency funding for coronavirus response and preparedness.

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They have also reached a deal on a $350 billion rescue package for small businesses that will feature federally guaranteed loans that will be fully refundable for employers who keep workers on payroll through the health crisis.

Senate Small Business Committee Chairman Marco Rubio Marco Antonio RubioSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Florida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll MORE (R-Fla.) told reporters the cost of the package could climb even higher as he and his colleagues wait on a cost estimate from the Congressional Budget Office.

“We’re now down to, how long will the money that’s being appropriated last? We want it to be long enough to get us through this period,” he said.

The interlocking nature of the negotiations means that no part of the sprawling bill is finalized until administration officials and senators agree to all of its parts.

While negotiators resolved some of their early disagreements, new problems popped up throughout the talks on Saturday as both sides upped their demands.

"The only thing is, when you keep adding at the last, within the last hour, or a couple things, as an example, then you have to go back and check on it. ... We've got a deadline," said Sen. Chuck Grassley Charles (Chuck) Ernest GrassleyGOP set to release controversial Biden report McConnell locks down key GOP votes in Supreme Court fight Senate Republicans face tough decision on replacing Ginsburg MORE (R-Iowa), describing the rolling nature of the negotiations.

Schumer and Sens. Ron Wyden Ronald (Ron) Lee WydenGOP set to release controversial Biden report Democrats fear Russia interference could spoil bid to retake Senate GOP senator blocks Schumer resolution aimed at Biden probe as tensions run high MORE (D-Ore.) and Elizabeth Warren Elizabeth WarrenGOP set to release controversial Biden report Biden's fiscal program: What is the likely market impact? Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (D-Mass.) on Saturday made a pitch to increase Social Security benefits, veterans assistance and Supplemental Security Income benefits by $200 a month.

A senior Senate GOP aide pointed to a Democratic demand to spend hundreds of billions of dollars on a state stabilization fund as a remaining sticking point. Democrats initially asked for $750 billion to help states, which Republicans refused, according to a person familiar with the talks.

Despite GOP hostility to an economic rescue of state governments, Republicans on Saturday acknowledged the final deal will include a “big number” to shore up state budgets.

Republicans, meanwhile, are seeking to dramatically increase funding to provide loans to distressed industries such as U.S. passenger airlines, air cargo carriers, hotel chains and energy companies.

Senate Banking Committee Chairman Mike Crapo Michael (Mike) Dean CrapoBottom line Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump Top GOP senator urges agencies to protect renters, banks amid coronavirus aid negotiations MORE (R-Idaho) said the $208 billion proposed in the original GOP plan to ensure distressed industries have access to capital should be increased to $300 billion, $400 billion or $500 billion.

He said augmenting Treasury Department funds to maximize the loan potential of the Fed would “inject much more capital” into the economy.

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Other items that remain unresolved are relief for student loans, where Democrats have proposed having the Department of Education make the payments on federal student loans for the duration of the coronavirus crisis. Republicans, in their initial plan, instead proposed deferring the payments.

White House Legislative Affairs Director Eric Ueland said Senate Health, Education, Labor and Pensions Committee Chairman Lamar Alexander Andrew (Lamar) Lamar AlexanderMcConnell locks down key GOP votes in Supreme Court fight Alexander backs vote on Trump Supreme Court nominee: What Democrats 'would do if the shoe were on the other foot' Toobin: McConnell engaging in 'greatest act of hypocrisy in American political history' with Ginsburg replacement vote MORE (R-Tenn.) would unveil “additional proposals” on student loans Sunday that have the president’s support.

Alexander, who is also in charge of the health care talks, declined to say if or how Republicans would address expanding paid sick leave — a priority for Democrats and Pelosi.

The Senate GOP plan introduced Thursday would give the secretary of Labor expanded authority to exempt businesses with fewer than 50 employees from paid sick leave benefits and creates caps for how much employers would pay under the sick leave proposal, a measure that was met with Democratic objection.

And in a curveball, Grassley tweeted on Saturday night that he “heard rumors” that the White House is trying to get legislation regarding surprise medical bills and health care tax extenders into the stimulus package.

Despite the litany of unresolved items, Senate Majority Leader Mitch McConnell (R-Ky.) appeared bullish as he spoke to reporters about the chances of getting a bipartisan deal.

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“We’re going to be able to produce a bipartisan agreement,” he said, predicting that it will pass the Senate on Monday.

He added in a subsequent statement that talks were ongoing but "very close to a resolution."

"I believe we are poised to deliver the significant relief that Americans need with the speed that this crisis demands," he said.

Senate Majority Whip John Thune John Randolph ThuneWhat Senate Republicans have said about election-year Supreme Court vacancies The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump contradicts CDC director on vaccine, masks MORE (R-S.D.) said that “there’s a lot of common ground” and that “on the main points everybody is kind of in the same place.” A GOP leadership aide predicted that there would not be “major setbacks” as negotiators work to bring the bill to a close.

Congress is under significant pressure to quickly pass the stimulus package to reassure the financial markets and the American public.

The U.S. has 25,493 confirmed cases of the virus as of Saturday evening, according to data from John Hopkins University, including 307 deaths.

Faced with an extreme time crunch, negotiators have resolved disagreements that might otherwise take weeks to iron out by simply agreeing to include both sides’ priorities — such as rebate checks and expanded unemployment insurance.

The total cost of the package has ballooned to between $1.5 and $2 trillion as both sides rush to cram their priorities into the package. The White House initially pitched a $1 trillion price tag, while Schumer called for at least $750 billion.

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Republicans are moving forward with drafting the bill even though they have not locked down an overall agreement. The text, according to senators and White House aides, will reflect bipartisan deals where they exist and ideas that Republicans believe could win over Democratic support for areas where they have not reached an agreement.

Talks over the unresolved areas are expected to continue ahead of Sunday’s procedural vote, where McConnell will need at least seven Democrats to vote to move forward even if they have not reached a deal.

"What the leader has instructed his committees to, with our support, is to finish drafting legislation that reflects agreements reached so far and that the chairman and the majority believe Democrats could be in a position to support by the time we vote," said Ueland.

McConnell added that he has asked committee chairmen to turn over legislative text on Saturday evening "that reflects their compromise products."

"This would allow all Senators to review the complete bipartisan text in advance of our first procedural vote at 3:00 p.m. tomorrow," he added.

Updated 9:41 p.m.