As Democrats celebrate the long-sought passage of Joe Biden’s sweeping health, climate and economic package, Bernie Sanders is not ready to declare victory. Instead, the Vermont senator is sounding the alarm that Congress has failed to meet the moment, with potentially grave consequences for American democracy.

“We are living in enormously difficult times,” he said in an interview with the Guardian. “And I worry very much … that people are giving up on democracy because they do not believe that their government is working for them.”

The legislation, which Biden is expected to sign into law next week, is but a sliver of the ambitious domestic policy initiative that Sanders, as chair of the Senate Budget Committee, helped draft last year. The original proposal was, in his view, already a compromise. But he believes it would have gone a long way in addressing the widespread economic distress that is undermining Americans’ faith in their government.

With control of Congress at stake this fall, Sanders believes Democrats squandered a major opportunity, probably their last before the midterm elections, to show voters what they could deliver with even larger majorities in Congress.

“It seems to me that what we should have done is gone forward with a bold agenda, to show the American people, ordinary people, that we understand what’s going on in their lives,” he said. “And if we cannot succeed because we don’t have the 50 votes, at least let the American people understand that we are fighting for them, and that we had to make a compromise to do far, far, far less than what is necessary.”

Sanders supported the resulting compromise, finalized after a year of strained negotiations and setbacks, because he concluded that “the pluses outweighed the negatives”.

A core pillar of the bill is nearly $400bn in climate and energy proposals, a historic sum that scientists estimate will help the US cut emissions by about 40% by the end of the decade, compared with 2005 levels. It also enables Medicare to negotiate the price of some prescription drugs, caps the annual out-of-pocket costs of the program’s beneficiaries at $2,000 and extends pandemic-era health insurance subsidies. To pay for it, the bill establishes a new 15% minimum tax on the nation’s biggest corporations.

But perhaps most notable, Sanders said, is what was left out.

Initially envisioned as a wholesale rebuilding of the American social safety net, weakened by decades of disinvestment, widening income inequality and stagnating wealth, the plan was slashed and trimmed and slashed again in an effort to appeal to two Democratic holdouts in the Senate, where the chamber’s even split left no margin for error.

Abandoned in the process were proposals to lower the cost of childcare, establish universal pre-K, guarantee parental leave, expand care for elderly and disabled people, and make community college tuition-free for two years. These policies, he argued, are the best way to begin easing the economic hardship facing so many American families.

To underscore his point, the senator listed a series of worrying indicators – elderly Americans unable to afford home care, families struggling to pay for childcare and young people burdened by student-loan debt, all of it made worse by soaring costs of necessities such as food, fuel and rent.

“A lot of people are hurting and they’re looking to the United States Congress, asking, ‘Do you understand what’s going on in my life right now?’” he said. “And I think their conclusion is no, they don’t.”

Sanders registered his dismay in a series of sharp floor speeches before the Senate vote last weekend, during which he decried Democrats’ plan as an “extremely modest bill that does virtually nothing to address the enormous crises facing the working families of our country”.

Another tradeoff that especially infuriated Sanders, and many climate activists, was the inclusion of fossil fuel and drilling provisions, which were added to win the support of Manchin, whose conservative state is heavily dependent on the coal and gas industries.

As heatwaves, floods and wildfires wreak havoc across the country, Sanders said: “Does anybody in their right mind think this is sensible, when you’re talking about climate?”

Yet he was optimistic that there had been a “change in consciousness” among lawmakers on the issue, partly because the effects were undeniable but also because of the actions of activists and young people.

“The activists should be proud,” he said, crediting their persistence for pushing Congress to make its largest ever investment in strategies to slow global warming.

During the Senate’s marathon, overnight debate – known as a “vote-a-rama” – Sanders offered a number of amendments that sought to restore some of the policies dropped from the original bill in an effort to win support from Joe Manchin of West Virginia and Kyrsten Sinema of Arizona. They included proposals to extend the child tax credit, expand Medicare coverage, cap the cost of prescription drugs and establish a civilian climate corps.

All were defeated, overwhelmingly: 1-99, 1-98, 1-97, with Sanders offering, he later quipped, the “resounding one” vote.

The votes frustrated some of his colleagues, who determined that Sanders’ approach risked upsetting their fragile coalition.

“Come on, Bernie,” Senator Sherrod Brown, Democrat of Ohio was overheard saying, after explaining that most Democrats supported the policies but were acting to preserve the broader deal.

Republicans, meanwhile, have derided the measure as reckless spending that would worsen not improve inflation. Sanders’ criticism of the bill as the “so-called Inflation Reduction Act” provided fodder for Republicans. “This won’t reduce inflation,” Republican senator Lindsey Graham, vice-chair of the Senate Budget Committee, said recently. “Just ask Bernie Sanders.”

Vice-President Kamala Harris cast the tie-breaking vote in the Senate on Sunday afternoon, and the House gave final passage the measure on Friday.

Acknowledging the political reality of Democrats thin majorities, Sanders argued that his Senate colleagues could have sent a strong message to voters by supporting his amendments, even if they were destined to fail.

“At this particular moment, we cannot leave it to conservative Democrats to define the direction in which Congress and the Democratic party is going,” Sanders said – an apparent reference to Manchin and Sinema.

Progressives in the House voiced similar reservations as Sanders, but ultimately saw the measure as the best chance to achieve some of their economic policy goals while Democrats control Congress. Ahead of the House vote on Friday, congresswoman Pramila Jayapal, a progressive from Washington, said there was much more to do but urged her colleagues to “celebrate this massive investment for the people”.

Biden declared the legislation a significant victory over “special interests”. “It required many compromises,” he said after the bill’s passage. “Doing important things almost always does.”

Sanders said the measure amounted to a “slight defeat” for Big Pharma – an industry, he noted, that counts as many as three lobbyists per member of Congress. But the senator said the prescription drug reforms were far too limited in scope, as the changes leave out most Americans, only apply to 10 drugs initially, and won’t take effect until 2026.

Senate Republicans rejected an amendment that would have capped insulin prices at $35 for Americans not on Medicare, a move Sanders said, “exposes the fraud for anyone who thinks the Republican party cares a damn about working people”.

Now as Democrats fan out across the country for the summer recess, many are testing a new pitch: touting their legislative success while asking voters to deliver them another, bigger congressional majority next year to accomplish what they could not this year.

With two more senators, Senate majority leader Chuck Schumer, said in a recent interview, “We would get childcare. We would get paid family leave. We would get help for the elderly, home care. We would get the kind of things that Joe Manchin was against.”

In the weeks ahead, Sanders said he plans to hit the trail for Democrats, with a blunter version of that message: “Give us two or three more seats so we don’t have to make compromises with corporate Democrats.”