Senate Republicans on Saturday took a crucial step toward passing their sweeping domestic policy bill, voting 51-49 to start debate on the legislation.

Two GOP senators — Rand Paul of Kentucky and Thom Tillis of North Carolina — joined Democrats to oppose advancing the cornerstone of President Donald Trump’s second-term agenda. But several others came around after hours of last-ditch negotiations to keep the bill moving forward.

The vote came after a daylong scramble by GOP leaders to win over several Republican senators who were viewed as undecided or had vowed to block debate over their opposition to pieces of the bill — including an extended negotiating session that unfolded with various senators and Vice President JD Vance while the vote was underway.

One of those senators, Ron Johnson of Wisconsin, said they won a promise of an amendment vote related to the expansion of Medicaid under the Affordable Care Act. Their proposal would end the 90 percent federal cost-share for new enrollees under that arrangement, Johnson said — gutting a key feature of the law known as Obamacare.

Senate Majority Leader John Thune declined to comment on the concessions, but Johnson suggested Thune and Trump will support the amendment, which has been promoted by Florida Sen. Rick Scott.

“The president’s pretty confident that whatever we pass here in the Senate, he’ll be able to convince people in the House to pass as well,” Johnson said.

Sen. Mike Lee of Utah, who was also part of the huddle, told reporters part of the conversation focused on deficit reduction. The Medicaid changes Johnson described would reap more savings. But they also risk sparking a fierce backlash from other corners of the party. Many GOP lawmakers have previously rejected the cost-sharing changes Scott has proposed.

Barring another blowup, the chamber is on a trajectory to pass the bill sometime Monday, though Thune cautioned in a brief interview he was not taking “anything for granted around here.”

Democrats are first forcing Senate clerks to first read the legislation out loud, which is expected to happen overnight, before a maximum 20 hours of debate plus a marathon series of amendment votes.

“Fifty-three members will never agree on every detail of legislation, let’s face it. But Republicans are united in our commitment to what we’re doing in this bill,” Thune said shortly before the vote. “It’s time to get this legislation across the finish line.”

Trump personally intervened Friday and Saturday to shore up the whip count. He aggressively lobbied Tillis on Friday night, according to a person granted anonymity to disclose private conversations. Tillis later confirmed the call, telling reporters he told Trump he could not support the bill because of the Medicaid language. Trump later attacked Tillis publicly and called for him to face a Republican primary challenger.

Johnson and Scott of Florida were at the White House shortly before the Senate’s vote. Johnson initially voted no, then went into a long stretch of negotiations with Thune, Vance and others alongside Sens. Cynthia Lummis of Wyoming, Lee of Utah and Scott of Florida. In the end, they emerged and voted to advance the bill just after 11 p.m.

By Saturday afternoon, it was clear to GOP senators that Vance would need to be on standby for what would be a nailbiter. He interceded after the vote was called to win over Alaska Sen. Lisa Murkowski, and then went to work on the other holdouts.

While enough GOP senators have voted to start debating the bill, it’s not yet assured there will be enough to pass it. Pieces of the bill remain in flux — not only due to Senate concerns, but also lingering opposition from some House Republicans. Several key issues, including the state-and-local-tax deduction and key Medicaid language, were addressed in updated text released late Friday night. But negotiations continue as leaders in both chambers work to ensure the Senate product can be passed in the House without changes and sent immediately to Trump’s desk.

Already GOP leaders have agreed to delay implementation of changes to a key Medicaid provision — a new cap on medical provider taxes, which most states use to fund their Medicaid programs — and have increased a rural hospital assistance fund from $15 billion to $25 billion.

Those changes were sufficient to win over Sen. Josh Hawley (R-Mo.), who announced Saturday he would support the bill. But it wasn’t enough to sway holdouts in both chambers concerned that the health care language could lead to hospital closures in their states and districts.

While Sen. Susan Collins of Maine supported starting debate, she described herself as “leaning against” final passage if the Medicaid provisions don’t change before a final vote. Collins said she planned to offer several amendments reflecting her concerns.

“It is the majority leader’s prerogative to determine which bills to bring to the floor,” she told reporters. “That does not mean in any way that I’m satisfied with the provisions in this bill.”

Tillis told reporters that he would be a “no” on the final vote, barring dramatic changes to the Medicaid provisions.

“It would result in tens of billions of dollars in lost funding for North Carolina, including our hospitals and rural communities,” he said in a statement. “This will force the state to make painful decisions like eliminating Medicaid coverage for hundreds of thousands in the expansion population, and even reducing critical services for those in the traditional Medicaid population.”

Johnson, Paul and Scott had each raised sharp concerns about the bill’s fiscal impacts, arguing it needed to cut more government spending. Paul, in particular, was deadset against its inclusion of a $5 trillion hike to the federal debt ceiling.

Republicans also made changes in the draft text released overnight to more aggressively phase out clean-energy tax credits established under former President Joe Biden in a bid to win over House conservatives. That prompted new attacks on the bill from Elon Musk, the erstwhile Trump ally, who called the megabill “utter madness” and “political suicide for the Republican Party.”

Democrats are expected to use the marathon amendment process, known as vote-a-rama, to try to water down the bill’s changes to the energy provisions, as well as Medicaid, federal food assistance and other key social safety net items.But first Democrats want to slow things down. By forcing clerks to read the 940-page bill aloud — a process that is typically waived — they hope to win more time to draw attention to the bill’s most unpopular provisions.

Senate aides estimate reading could take about 15 hours, pushing final passage from Sunday into Monday unless Democrats unexpectedly yield back a significant amount of their debate time.

“Senate Republicans are scrambling to pass a radical bill, released to the public in the dead of night, praying the American people don’t realize what’s in it,” Minority Leader Chuck Schumer said. “If Senate Republicans won’t tell the American people what’s in this bill, then Democrats are going to force this chamber to read it from start to finish.”

Katherine Tully McManus and Lisa Kashinsky contributed to this report.