Senators resumed a weekend session toward passage of a $1tn bipartisan infrastructure package on Sunday amid threats from former president Donald Trump who raged against any Republicans who support the measure.

Majority leader Chuck Schumer stressed to colleagues that they could proceed the “easy way or the hard way”, while a few Republican senators appeared determined to run out the clock for days. “We’ll keep proceeding until we get this bill done,” Schumer said.

The bill would provide what Joe Biden has called a “historic investment” in public works programs, from roads and bridges to broadband internet access, drinking water and more. It was expected to pass on Saturday – before it heads to the House – but ran into Republican procedural delays, forcing yet another day of debate.

Trump, who maintains a strong grip on the party and intense popularity with much of its base, also throw a spanner in the works by attacking any of his party who back the bill.

“Joe Biden’s infrastructure bill is a disgrace,” he said in a statement and then added that it “…will be very hard for me to endorse anyone foolish enough to vote in favor of this deal.”

In a rare stroke of bipartisanship, Republicans joined Democrats to advance the measure and more votes are expected Sunday. If approved, the bill would go to the House, where it might face changes and – if it does – it could return to the Senate for another vote before heading to Biden’s desk.

Despite the overwhelming support, momentum has dragged as a few Republican senators refused to yield 30 hours of required debate before the next set of procedural votes, which could delay swift passage of the package and result in a dayslong slog.

Senators were meeting for the second consecutive weekend to work on the Infrastructure Investment and Jobs Act, which is the first of Biden’s two infrastructure packages.

Once voting wraps up, senators immediately will turn to the next item on Biden’s agenda, the budget outline for a $3.5tn package of child care, elder care and other programs that is a much more partisan undertaking and expected to draw only Democratic support.

Schumer has vowed to keep senators in session until they finish up the bipartisan bill and start the initial votes on the next big package.

For some Republican senators, the back-to-back voting on Biden’s big priorities is what they are trying to delay, hoping to slow or halt what appears to be a steady march to achieve the president’s infrastructure goals.

Senator Bill Hagerty of Tennessee, an ally of Donald Trump and the former president’s ambassador to Japan, was among those leading the effort for the Senate to take as much time as needed to debate and amend the bill.

“There’s absolutely no reason to rush,” Hagerty said during a floor speech Saturday.

Senate Republican leader Mitch McConnell of Kentucky has so far allowed the bill to progress and backed it, despite the broadsides and name-calling coming from Trump. “This is a compromise,” McConnell said.

Senators have spent the past week processing nearly two dozen amendments to the 2,700-page package, but so far none has substantially changed its framework.

More amendments could be debated Sunday with senators considering revisions to a section on cryptocurrency, a long-shot effort by defense hawks to add $50bn for defense-related infrastructure and a bipartisan amendment to repurpose a portion of the untapped Covid-19 relief aid that had been sent to the states.