WASHINGTON (AP) — Edging toward a vote, senators are convening for a rare weekend session on the bipartisan infrastructure bill, which could wrap up swiftly with passage of the $1 trillion package or drag out for days by opponents trying to slow President Joe Biden’s big priority.

The president nudged senators along from the White House, praising their work so far as a potentially “historic investment” — on par with the building of the transcontinental railroad or interstate highway system — that will bring jobs and modernization to millions of Americans.

Senators appear on track to approve the bill, despite days of fits and starts.

“It’s a bill that would end years of gridlock in Washington and create millions of good-paying jobs, put America on a new path to win the race for the economy in the 21st century,” Biden said Friday.

Saturday’s session will launch with a crucial 60-vote hurdle at midday that will determine if the bipartisan alliance between Republicans and Democrats holds on the public works package. Ten Republicans would be needed to join all Democrats to advance it past a filibuster; more votes would follow.

Senate Republican leader Mitch McConnell has so far allowed the bill to progress, and his vote will be one to watch. Senate Majority Leader Chuck Schumer, D-N.Y., has vowed to keep senators in session until they finish.

Called the Infrastructure Investment and Jobs Act, the thick bill is a first part of Biden’s infrastructure agenda. It would inject $550 billion of new spending over the next five years on roads, bridges, waterworks, broadband and other projects to virtually every corner of the nation. If approved by the Senate, it would next go to the House.

For senators who have been slogging through debate — and months of give-and-take negotiations — it’s a chance not only to send federal funds to their states, but also to show the country that Congress can work together in a bipartisan way to solve problems.

Republican Sen. Lisa Murkowski said the needs back home in Alaska are obvious — including money for water systems in remote villages without running taps for handwashing during the COVID-19 pandemic. But as one of the negotiators, she also wants to demonstrate that lawmakers can reach across the aisle to govern.

“I’m really worried that everybody believes that we’re as dysfunctional as we appear to be, and so to prove otherwise, it’s kind of important,” she said. “The Senate needs some demonstrated acts of bipartisanship.”

The weekend action comes as Congress is under pressure to make gains on the president’s infrastructure priorities — first with the bipartisan bill that’s on track for passage as soon as this weekend, and quickly followed by Democrats’ more sweeping $3.5 trillion budget blueprint they plan to shoulder on their own.

If senators wrap up work on the bipartisan bill, they immediately will turn to the much more partisan undertaking on Biden’s agenda, the outline for the $3.5 trillion proposal. That plan would unleash billions on what the White House calls human infrastructure — child care support, home health care, education and other expenditures that are Democratic priorities that Republicans have pledged to reject. Debate on that will extend into the fall.

Schumer has vowed to show progress on both before recessing the Senate for August.

For some Republicans, that back-to-back voting schedule is what they are trying to delay, hoping to slow or halt what appears to be a forward march by Democrats to make gains on the president’s infrastructure goals.

Sen. Bill Hagerty, R-Tenn., an ally of Donald Trump’s who had been the former president’s ambassador to Japan, said he objected to expediting consideration of the bill.

“I could not, in good conscience, allow that to happen,” Hagerty said in a statement early Friday. He said he was especially concerned that passing the bipartisan bill would pave the way for Democrats to move quickly to their $3.5 trillion “tax-and-spend spree.”

Overall, the infrastructure bill calls for billions in new spending above projected federal levels to create a nearly $1 trillion package, in what could be one of the more substantial investments in years.

Senators had hoped to wrap up the 2,700-page bipartisan bill late in the week before many of them departed to attend funeral services Friday in Wyoming for former Sen. Mike Enzi, a Republican.

But the Senate ground to a halt with new problems as senators worked late into the night Thursday on amendments and to counter objections from Republican opponents of the plan to expedite the process.

An analysis of the bill from the Congressional Budget Office drew concerns, particularly from Republicans. It concluded that the legislation would increase deficits by about $256 billion over the next decade.

But the bill’s backers argued that the budget office was unable to take into account certain revenue streams — including from future economic growth.

Paying for the package has been a pressure point throughout the monthslong slog of negotiations after Democrats objected to a hike in the gas tax paid at the pump and Republicans resisted a plan to beef up the IRS to go after tax scofflaws.

Unlike Biden’s bigger $3.5 trillion package, which would be paid for by higher tax rates for corporations and the wealthy, the bipartisan package is funded by repurposing other money, including untapped COVID-19 aid, and other spending cuts and revenue streams.

Senators have spent the past week processing nearly two dozen amendments to the bipartisan package, with more possible on Saturday. So far, none has substantially changed the framework of the public works package.

One of the amendments generating the most attention involves cryptocurrency.

The bill would raise an estimated $28 billion over 10 years by updating IRS reporting requirements for cryptocurrency brokers, just as stockbrokers report their customers’ sales to the IRS.

Sen. Pat Toomey, R-Pa., and others who wanted to narrow the definition of who must file those IRS forms are concerned that crypto miners, software developers and others would be subject to the new reporting requirement.

Toomey warned that the provision, as written, could have a “chilling effect on the development of this technology.”

The White House weighed in late Thursday, suggesting it favored a different approach from Sen. Rob Portman, R-Ohio, Sen. Mark Warner, D-Va., and other senators.

White House deputy press secretary Andrew Bates said the compromise amendment “would reduce tax evasion in the cryptocurrency market.”

The House is away on recess and is expected to consider both Biden infrastructure packages when it returns in September.

House Speaker Nancy Pelosi, D-Calif., reiterated that her chamber will consider the infrastructure bills “together.”