WASHINGTON (AP) -- After a weekend of setbacks, the Senate will try to sprint ahead Monday on President Donald Trump's big bill of tax breaks and spending cuts despite a series of challenges, including the sudden announcement from one GOP senator that he won't run for reelection after opposing the package over its Medicaid health care cuts.

An all-night session to consider an endless stream of proposed amendments to the package, in what's called a vote-a-rama, was abruptly postponed, and it's now scheduled to launch as soon as the Senate gavels open. With Democrats united against the Republican president's legislation and eagerly lined up to challenge it, the voting could take all day.

Senate Democratic Leader Chuck Schumer of New York said the "hardest choices" for Republicans are still to come. His side plans to bring "amendment after amendment after amendment to the floor, so Republicans can defend their billionaire tax cuts and so they can try to explain their massive cuts to Medicaid to people back home."

The hours ahead will be pivotal for the Republicans, who have control of the Congress and are racing against Trump's Fourth of July deadline to wrap up work. The 940-page "One Big Beautiful Bill Act," as it is now formally titled, has consumed the Congress as its shared priority with the president, with no room politically to fail, even as not all Republicans are on board.

A new analysis from the nonpartisan Congressional Budget Office found that 11.8 million more Americans would become uninsured by 2034 if the bill became law. It also said the package would increase the deficit by nearly $3.3 trillion over the decade.

House Speaker Mike Johnson's leadership team has recalled lawmakers back to Washington for voting in the House as soon as Wednesday, if the legislation can first clear the Senate.

But the outcome remains uncertain, especially after a weekend of work in the Senate that brought less visible progress on securing enough Republican support, over Democratic opposition, for passage.

Few Republicans appear fully satisfied as the final package emerges. GOP Sen. Thom Tillis of North Carolina, who announced Sunday he would not seek reelection after Trump badgered him over his opposition to the package, said he has the same goals as Trump, cutting taxes and spending.

But Tillis said this package is a betrayal of the president's promises not to kick people off health care, especially if rural hospitals close.

"We could take the time to get this right," he thundered.

At the same time, some loosely aligned conservative Senate Republicans -- Rick Scott of Florida, Mike Lee of Utah, Ron Johnson of Wisconsin and Cynthia Lummis of Wyoming -- have pushed for steeper cuts, particularly to health care, drawing their own warning from Trump.

"Don't go too crazy!" the president posted on social media. "REMEMBER, you still have to get reelected."

GOP leaders barely secured enough support to muscle the legislation past a procedural Saturday night hurdle in a tense scene. A handful of Republican holdouts revolted, and it took phone calls from Trump and a visit from Vice President JD Vance to keep it on track.

As Saturday's vote tally teetered, attention turned to Sen. Lisa Murkowski, R-Alaska, who was surrounded by GOP leaders in intense conversation. She voted "yes."

Several provisions in the package including a higher tax deduction for native whalers and potential waivers from food stamps or Medicaid changes are being called the "Polar Payoff" designed for her state. But some were found to be out of compliance with the rules by the Senate parliamentarian.

All told, the Senate bill includes some $4 trillion in tax cuts, making permanent Trump's 2017 rates, which would expire at the end of the year if Congress fails to act, while adding the new ones he campaigned on, including no taxes on tips.

The Senate package would roll back billions of dollars in green energy tax credits that Democrats warn will wipe out wind and solar investments nationwide and impose $1.2 trillion in cuts, largely to Medicaid and food stamps, by imposing work requirements, making sign-up eligibility more stringent and changing federal reimbursements to states.

Additionally, the bill would provide a $350 billion infusion for border and national security, including for deportations, some of it paid for with new fees charged to immigrants.

Unable to stop the march toward passage, the Democrats as the minority party in Congress are using the tools at their disposal to delay and drag out the process.

Democrats forced a full reading of the text, which took 16 hours. Then Democratic senators took over Sunday's debate, filling the chamber with speeches, while Republicans largely stood aside.

"Reckless and irresponsible," said Sen. Gary Peters, a Democrat from Michigan.

"A gift to the billionaire class," said Vermont's Sen. Bernie Sanders, an independent who caucuses with Democrats.

"Follow what the Bible teaches us: Do unto others as you would have them do unto you," said Sen. Ben Ray Lujan, D-N.M., as Sunday's debate pushed past midnight.

Sen. Patty Murray of Washington, the ranking Democrat on the Appropriations Committee, raised particular concern about the accounting method being used by the Republicans, which says the tax breaks from Trump's first term are now "current policy" and the cost of extending them should not be counted toward deficits.

"In my 33 years here in the United States Senate, things have never -- never -- worked this way," said Murray, the longest-serving Democrat on the Budget Committee.

She said that kind of "magic math" won't fly with Americans trying to balance their own household books.

"Go back home," she said, "and try that game with your constituents."

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Associated Press writers Ali Swenson, Fatima Hussein and Michelle L. Price contributed to this report.