Washington — The Senate debated President Trump's massive tax bill into early Monday. Votes are scheduled for Monday morning, as Republicans try to pass the centerpiece legislation of Mr. Trump's second term agenda.

The House narrowly passed the bill last month, and Senate Republicans have been working to put their mark on the legislation, treading carefully so as not to throw off the delicate balance in the lower chamber. The House will need to approve the Senate's changes to the bill before it can head to the president's desk for his signature. And lawmakers are trying to move quickly, with a self-imposed July 4 deadline to get the measure signed. 

The Senate worked through the weekend as the GOP nears a final sprint on the legislation ahead of the deadline. Titled "One Big, Beautiful Bill," the legislation includes increased spending for border security, defense and energy production, which is offset in part by cuts to healthcare and nutrition programs. The Congressional Budget Office estimated Sunday that the legislation would increase the deficit by nearly $3.3 trillion over the next decade.

Senate Republicans advanced the legislation late Saturday, with all but two voting in favor following hours of delay as the GOP worked to iron out last-minute details and dispel concern among holdouts. The vote on the motion to proceed stayed open for more than three hours as holdouts sought assurances from GOP leaders. Some tweaks were made to the bill before Republicans ultimately received enough votes to move forward.

Senate Democrats further delayed the legislation's path forward by forcing the bill to be read in its entirety, starting late Saturday. After nearly 16 hours, the Senate clerks concluded their reading of the bill on the floor, starting the clock on debate. Each side then had 10 hours for debate. Democrats were expected to use all of their time to rail against the legislation. 

Senate Republicans have been pursuing the legislation through the budget reconciliation process, which enables the party in the majority to move ahead without support from across the aisle. With only a simple majority required to advance the measure, rather than the 60-votes needed to move forward with most legislation, Senate Democrats have few mechanisms to combat the bill's progress. 

Following debate, the Senate is set to begin a "vote-a-rama," in which senators could offer an unlimited number of amendments and force the chamber to cast vote after vote. That process was originally expected to begin in the early morning hours on Monday, but Senate leadership said late Sunday that once debate concluded, the Senate would not reconvene until 9 a.m. ET Monday. Democrats are expected to use the opportunity to put their GOP colleagues on the record on a number of controversial issues ahead of the midterm elections.

With a 53-seat majority, Senate GOP leaders can only afford to lose support from three Republicans — and would then still require a tie-breaking vote from Vice President JD Vance. And although a number of senators who had expressed opposition to the measure ultimately decided to advance it Saturday, how they will vote on the measure in a final form remains unclear. 

Senate Majority Leader John Thune said Saturday that "it's time to get this legislation across the finish line," adding that "53 members will never agree on every detail of legislation." But he urged that Republicans are "united in our commitment to what we're doing in this bill."

Vance was on hand to break a possible tie vote Saturday, though his vote ultimately wasn't needed. Still, the vice president met with GOP holdouts in the majority leader's office Saturday as the White House put pressure on lawmakers to get the bill across the finish line.

Meanwhile, Sen. Mark Warner, a Virginia Democrat, warned Sunday that the legislation would be a "political albatross" for Republicans, while suggesting that the bill could even lose support among the GOP, saying "it's not over until it's over."

"I think many of my Republican friends know they're walking the plank on this, and we'll see if those who've expressed quiet consternation will actually have the courage of their conviction," Warner said Sunday on "Face the Nation with Margaret Brennan."