Joe Biden sought to brush off concerns about bad polling on Sunday, telling reporters he expected Democrats to overcome internal differences and pass both his domestic spending plan and a bipartisan infrastructure deal in the week to come.

Earlier, an NBC News poll found that 54% of US adults disapproved of Biden’s performance, down six points since August, a period in which the president’s domestic agenda has stalled amid intra-party division.

Biden spoke to reporters in Rome at the end of the G20, before traveling to Glasgow for the Cop26 climate summit.

He said: “I didn’t run to determine how well I’m going to do in the polls. I ran to make sure that I follow through on what I said I would do as president of the United States.

“I said that I would make sure that we were in a position where we dealt with climate change, where we moved in a direction that would significantly improve the prospects of American workers having good jobs and good pay. And further that I would make sure that we dealt with the crisis that was caused by Covid.

“… I believe we will pass my Build Back Better plan. I believe we will pass the infrastructure bill. Combined, they have $900bn in dealing with climate resilience, the largest investment in the history of the world that’s ever occurred. And it’s going to pass in my view, but we’ll see. We’ll see.”

Biden has staked his presidency on his spending plans but Democrats in Congress have been split between progressives and moderates led by two senators, Joe Manchin of West Virginia and Kyrsten Sinema of Arizona. Biden delayed his departure to Rome to plead with Democrats to pass his spending agenda.

“We are at an inflection point,” he reportedly told House members. “The rest of the world wonders whether we can function.”

Whether Democrats can deliver could also have significant implications for the midterm elections next year. Historically, parties holding the presidency fail to keep the House.

Top Democrats reportedly want a final version of Biden’s $1.75tn spending plan drafted by Sunday and passed by Tuesday. The price tag has come down dramatically, from $3.5tn, with concessions to Manchin and Sinema. The infrastructure deal is valued at $1tn.

Discussions continued throughout the weekend. Bernie Sanders, the chair of the Senate budget committee, told CNN’s State of the Union: “I can tell you, we are working right now. I spent all of yesterday on the telephone … as soon as I leave the studio, I’m going to be going back home to get on the phone.”

Sanders said he was optimistic and added: “This is not easy stuff, but what we are trying to do is put together the most consequential piece of legislation in the modern history of this country, which will transform the role of government in protecting the needs of working families.”

Sanders said he was fighting for action on prescription drugs costs to be included in the spending bill, an issue on which he and Sinema are in very evident opposition.

In a 50-50 Senate, and with no Republican support on spending, Manchin and Sinema are key. Democrats must use reconciliation, a way to pass budgetary initiatives via a simple majority rather than 60 votes. The vice-president, Kamala Harris, has the decisive vote.

The Senate did pass the infrastructure bill in August via a bipartisan vote but House progressives stymied it in an attempt to win concessions on the spending plan. On Sunday Ro Khanna of California, a prominent House progressive, told CBS’s Face the Nation he expected success.

“We are working to add things in,” he said. “The negotiations are taking place. I’m going to be a yes. I think we can have the vote by Tuesday … I’m yes on the framework.”

Cabinet members also expressed optimism. The transportation secretary, Pete Buttigieg, told Fox News Sunday: “We are teed up for major action soon.”

Asked if Congress would pass both pieces of legislation this week, he said: “We are the closest we have ever been.”

Buttigieg also made a point sure to surface in the midterms if Biden is successful, telling ABC’s This Week he “wouldn’t let Republicans off the hook on voting for the family provisions too.

“I know they probably won’t but it’s not too late for some of them to join Democrats who are united in believing that the time has come for us to actually put our money where our mouth is [and] support American families.”

A Republican senator, Rick Scott of Florida, told Fox News Sunday Biden’s spending had “to end” as it was “causing inflation” and “hurting the poor families”.

“We gotta live within our means like every family does,” Scott said.

Asked if that meant Republicans should support repeal of tax cuts they passed under Donald Trump which are projected to add $2tn to the national debt, Scott said both taxes and spending should be cut.

On NBC’s Meet the Press the energy secretary, Jennifer Granholm, suggested Biden’s polling would be boosted when Americans see his spending bill.

“They’ll see that they’re going to get a continuation of that child tax credit,” Granholm said. “They’ll see people being put to work in clean energy all across this country.

“They’re going to see the ability to have senior citizens and people with disabilities being cared for in their homes. They’ll see their costs of living come down as a result of having children. This bill and the real impacts that people will see will have an impact on those ratings.”

In Rome, Biden told reporters: “You know, you all believed [the spending bill] wouldn’t happen from the very beginning, the moment I announced it, and you always seem amazed when it’s alive again. Maybe it won’t work. But I believe we’ll see by the end of next week at home that the bills have passed.”

• The Associated Press contributed to this report