Senate Democrats slog through marathon voting session with their $740 billion climate and tax bill nearing the finish line

• Senate Democrats kicked off a marathon voting session late Saturday night.
• As of Sunday morning, senators have been voting for nearly seven hours.

Senate Democrats, early Sunday morning, are slowly moving toward passage of their $740 billion climate, healthcare, and tax bill.

Senators are nearing almost seven hours of marathon voting in the thick of a "vote-a-rama," a procedural quirk that allows lawmakers to propose endless amendments to the point of exhaustion.

The package — mostly hammered out between Senate Majority Leader Chuck Schumer of New York and Sen. Joe Manchin of West Virginia — includes a raft of measures.

It would allow Medicare to negotiate the price of some prescription drugs, establish over $300 billion in clean-energy tax credits, and extend financial assistance so Americans can purchase health coverage under the Affordable Care Act for three more years.

Repeated delays meant that senators did not begin their vote-a-rama until 11:31 pm Saturday in Washington. The bill's final passage is expected sometime Sunday, but it's unclear how long senators will continue the slow grind of amendment votes. As of 6:15 am, they have gone through 16 amendments and other procedural steps that have sought to derail the bill.

Before voting began, Senate Republicans vowed to force Democrats to take politically painful votes, part of an effort to exploit those positions for the November midterms.

"What will vote-a-rama be like? It will be hell," Sen. Lindsay Graham of South Carolina told reporters on Friday. "These are going to be hard votes for the Democrats."

GOP lawmakers have made good on their promise to offer politically dicey votes, following through with votes on immigration, oil taxes, the size of the IRS, and crime-related measures. So far, Democrats have stayed mainly united and avoided changing the overall legislation, which could complicate or even doom the proposal.

Sen. Bernie Sanders, a Vermont independent, followed through on his days-long criticism of the bill. Sanders forced three votes, though he has largely ended up isolated. The one exception was when he offered an amendment requiring Medicare to cover dental, vision, and hearing benefits. But only Georgia Democrats, Sens. Raphael Warnock and Jon Ossoff, joined him.

The most contentious moment came late Saturday night when Sen. Maggie Hassan of New Hampshire sought to offer her fellow Democrats a way to claim that they tried to eliminate a proposed oil tax increase in the overall legislation.

Republican Sen. Lindsey Graham of South Carolina tore into Hassan to the point that her Democratic colleagues began booing him. Eventually, four other Democrats, Sens. Catherine Cortez-Masto, Mark Kelly, Ralphael Warnock, and Kyrsten Sinema, joined her to advance the failed amendment.

Some senators told reporters as dawn broke that their colleagues were growing tired, but others had found ways to squeeze in a few brief naps throughout the evening.

"I'm awake now, I get up at 4," Iowa Sen. Chuck Grassley, the chamber's oldest Republican, told reporters around 7 a.m, adding that he had taken naps at roughly 10-minute intervals during late-night votes.

Grassley was among a pair of Republicans who sparked criticism for appearing to complain about being forced to stay in town.

"Each Dec Schumer puts out schedule for Senate I set Grassley family reunion based on schedule," Grassley wrote on Twitter. "For 2nd yr in row I won't be at reunion I'm in DC to fight Dems irresponsible tax&spend bill."

While Sen. Marco Rubio of Florida complained about his schedule being upended by a "garbage bill."

"Woke up at 5 am to a 3 am email that my 8:30 am flight was cancelled but they rebooked me on an 8 pm flight tomorrow night with one connection," Rubio, a former 2016 presidential hopeful, wrote on Twitter, "Now in DC for the joy that is 'vote a rama' on a garbage bill."

The vote-a-rama is a special part of the Senate procedure required because Democrats want to muscle through their plan without a single Republican vote under a budget reconciliation process.

It allows Democrats to blow past the usual obstacle of the filibuster and its 60-vote threshold that effectively kills most legislation. In turn, minority parties use the vote-a-rama to damage their political opponents since they cannot resort to the usual protection of the filibuster.

Unlike Grassley, Sen. James Inhofe, who is retiring next year, said he could not afford to squeeze in naps.

"I don't take naps, if I fall asleep I'm gone," Inhofe, who is 87, told reporters before taking in a brief moment of fresh air.

Much attention was focused on Sen. Patrick Leahy, the longest-serving Democrat in the chamber, who has mostly been away from the Senate following a fall and emergency hip replacement. After a long night of voting, Leahy told reporters that he was feeling fine.

"'Pat, I'm glad you're here, we shouldn't have to suffer alone,'" Leahy told reporters that Sen. Tim Kaine, a Virginia Democrat, said to him.