Joe Biden returned to the US in the pre-dawn gloom on Wednesday to a climate agenda still held in frustrating limbo by Congress, following his high-profile cameo at crunch UN climate talks in Scotland that was heavy on dire warnings but light on deep cuts to planet-heating emissions.

The US president had aimed to arrive in Glasgow for the Cop26 summit with historic climate legislation in hand, which he could use to brandish at world leaders who still harbor resentments over four turbulent years of Donald Trump, where the climate crisis was variously ignored and mocked.

Instead, the intransigence of Senator Joe Manchin, a centrist Democrat and leading beneficiary of fossil fuel industry largesse, has left the landmark climate bill pared back and not voted upon, its fate left uncertain throughout Biden’s trip.

In Glasgow, Biden vowed America will “lead by the power of our example”, but was the target of activist protests over oil and gas leases issued back home, while leaders of several major emitters either did not show up or failed to submit vastly improved emissions reduction plans.

Biden ended his time in Scotland by ladling blame upon China for not taking the climate emergency seriously.

“The most important thing the president needed to do was reassure the rest of the world that the US is back in addressing this global crisis,” said Christy Goldfuss, an environment adviser to Barack Obama and now a policy expert at the Center for American Progress.

“But we have to have some humility, we have ground to make up. We can’t reclaim the mantle of leadership until the US can deliver on its commitments. Every Democrat, apart from one senator, supports climate action. That is untenable and everyone understands that.”

Biden has sought to play up the positives of his time at Cop26, where he has left negotiators to thrash out a deal aimed at averting disastrous global heating of beyond 1.5C. “I can’t think of any two days where more has been accomplished on climate,” he said.

The highlights include a global pledge, led by the US and European Union, to slash methane, a potent greenhouse gas, by 30% by 2030, based on last year’s levels. More than 100 countries, including six of the 10 largest emitters of methane, have signed on to the agreement to cut methane, which is spewed out by oil and gas drilling operations and agriculture and is about 80 times more powerful in trapping heat than carbon dioxide.

Biden backed this move with new regulations rolled out by the US Environment Protection Agency to cut methane emissions by about 75% from hundreds of thousands of oil and gas wells. “The pledge to cut methane is the single biggest and fastest bite out of today’s warming,” said Durwood Zaelke, president of the Institute for Governance and Sustainable Development.

There was also a sweeping accord, which Biden vowed to support with billions of dollars, to end deforestation within a decade. The pact encompasses 85% of the world’s forests, vital for biodiversity and to soak up excess carbon from the atmosphere, and is backed by Brazil, Russia and China, countries often reluctant to make such promises.

But the US was clearly piqued at how little the relentless diplomacy of John Kerry, Biden’s climate envoy, had done to extract deeper emissions cuts from leading carbon polluters. Neither Russia’s Vladimir Putin nor China’s Xi Jinping, who both offered barely improved new targets at the talks, traveled to Glasgow. Biden’s frustration bubbled over as he prepared to depart on Tuesday.

“The fact that China is trying assert a new role in the world as a world leader, not showing up? Come on,” Biden said. “It’s just a gigantic issue and they’ve walked away. How do you do that and claim to have any leadership now? Same with Putin in Russia: his tundra is burning. Literally his tundra is burning. He has serious, serious climate problems and he’s mum on his willingness to do anything.”

The blame placed at Cop upon China, which is now the world’s largest emitter of greenhouse gases, comes amid frayed US-China relations on several fronts. The Global Times, a newspaper run by China’s Communist party, said in an editorial that Washington’s attitude had made it “impossible for China to see any potential to have fair negotiation amid the tensions”.

Goldfuss said: “The blame game is not something the US should be really playing right now given we have so much work to do ourselves.”

Back home, Biden has acknowledged his presidency will probably be defined by the proposed reconciliation bill that contains $555bn in climate measures. The White House says the legislation would bring the country close to the president’s goal of cutting emissions in half this decade and help curb disastrous climate breakdown that is already unleashing severe heatwaves, floods and drought at home and around the world.

The far-reaching legislation needs every Democratic vote to pass the Senate but West Virginia’s Manchin has questioned its scope, said it is filled with “gimmicks” and has already ensured that a centerpiece plan to phase out fossil fuels from the American electricity grid was axed from the bill.

Democrats continue to fret over the fate of the bill, with a vote that could take place as early as this week, with Biden saying he is “confident we will get it done”. But climate campaigners say the president could do more without the help of Congress to stem the flow of fossil fuels that are causing the climate crisis.

The opening week of Cop26 saw Biden’s administration announce it will sell off oil and gas drilling leases across 730,000 acres of the US west, with a further auction of 80m offshore acres of the Gulf of Mexico, an area larger than the UK, set to commence later this month. The International Energy Agency has said that no new fossil fuel projects can commence if the world is to keep to the agreed 1.5C warming limit.

“With all eyes on Glasgow this week, the Biden administration seems to be turning its back on reality and throwing climate leadership into the toilet,” said Jeremy Nichols, climate and energy program director for WildEarth Guardians.