The Senate is plowing ahead toward a final vote on President Donald Trump’s sweeping tax and immigration bill, as Republicans rush to get it across the finish line by July 4.

The self-imposed deadline by Trump meant a rare weekend session for lawmakers, one filled with partisan drama and some GOP infighting on the “One Big Beautiful Bill Act.”

On Monday morning, senators began a “vote-a-rama” — votes on proposed amendments to the megabill.

There is no limit to the number of amendments lawmakers can seek. Senate Minority Leader Chuck Schumer, the chamber’s top Democrat, promised his party would bring amendment after amendment during the marathon session. Democrats forced a reading of the 940-page bill over the weekend, which took nearly 16 hours.

“Every senator will soon have an opportunity to reject this nonsense and vote for common-sense budgeting. Americans will be watching,” Schumer said on Monday as he slammed Trump’s bill as a break for billionaires that will hurt working-class families.

Senate Majority Leader John Thune defended the bill as delivering Trump’s campaign promises to eliminate tax on tips and overtime pay while boosting spending for defense and border security.

“It’s been a long debate,” Thune said in his own floor remarks ahead of the votes on amendments. “I know people are weary. But at the end of the day, we want to get this done so that this country is safer and stronger and more prosperous, not only for today but for future generations of Americans.”

The vote-a-rama is the last hurdle before a vote on final passage of the bill in the Senate.

There is little room for error in the Republican-controlled chamber. A procedural vote on Saturday night to open debate on the bill narrowly passed in a 51-49 vote after two Republican defections.

GOS Sens. Rand Paul of Kentucky and Thom Tillis of North Carolina voted against advancing the bill. Tillis railed against the changes to Medicaid in the bill, saying it would hurt his constituents and would represent a betrayal of Trump’s promise not to touch the entitlement program upon which millions of people rely for health care coverage.

Tillis’ opposition drew Trump’s ire, with the president threatening to support a primary challenger to the two-term senator. Tillis then suddenly announced he would not seek reelection, saying later he texted Trump on Saturday night suggesting he “probably needed to start looking for a replacement.”

“I respect President Trump. I support the majority of his agenda, but I don’t bow to anybody. When the people of North Carolina are at risk. And this bill puts them at risk,” Tillis said.

What’s next for OBBB in the House?

If the “One Big Beautiful Bill Act” passes in the Senate, it will have to go back to the House for members to consider the changes made to the bill.

House Republican leaders say Wednesday is the earliest chance for a megabill vote.

“Members are advised that votes are now expected in the House as early as 9 a.m. Wednesday, July 2. Please stay tuned to future updates for additional information regarding this week’s schedule,” a notice from Majority Whip Tom Emmer’s office said.

Republican leaders have told members they will receive 48 hours notice before a vote is called and will have 72 hours to review the bill text.

The House passed the Trump megabill by just one vote back in May. The Senate version of the bill will face an uphill battle in the House, given the GOP’s razor-thin majority.

California moderate Republican Rep. David Valadao said he will vote no given the Medicaid changes in the Senate bill. Several conservatives, including Reps. Chip Roy of Texas, Josh Breechen of Oklahoma and Eric Burlison of Missouri have also expressed opposition to the Senate’s version of the bill.

House Speaker Mike Johnson and other Republican leaders worked through the weekend to lock down the votes even as several lawmakers have expressed opposition to the Senate’s version, which is still not finalized. Johnson can only afford to lose 3 defections if all members are voting and present.

ABC News’ Alexandra Hutzler contributed to this report.