GLASGOW, Scotland — President Biden argued Tuesday that historic progress on addressing global warming was achieved at the U.N. climate conference in Glasgow, Scotland, and expressed optimism for a similar outcome in Washington, where his legislative agenda has been stalled by intra-party disagreements.

Speaking in a press conference before boarding Air Force One to return to Washington, Biden highlighted new efforts to stop methane leaks, protect forests, invest in new technologies and spend money on clean energy infrastructure. But his efforts to meet U.S. commitments on climate change with a major domestic spending bill remained held up by legislative maneuvering.

“I can’t think of any two days where more has been accomplished on climate than these two days,” Biden said.

The president contrasted the U.S. posture of leading several major initiatives at the summit with those of Russia and China, who did not send their leaders to Glasgow. Biden called that “big mistake.”

“We showed up. We showed up,” Biden said. “And by showing up we’ve had a profound impact, I think, on how the rest of the world is looking at the United States.”

Biden has been determined to demonstrate to the world that the U.S. is back in the global effort against climate change, after his predecessor Donald Trump pulled the U.S. – the world’s largest economy and second-biggest climate polluter – out of the landmark 2015 Paris climate accord.

Putting the U.S. on the path to halve its own output of coal, oil and natural gas pollution by 2050, as his climate legislation seeks to do, “demonstrates to the world the United States is not only back at the table, it hopefully can lead by the power of our example,” Biden told delegates and observers on Monday.

“I know that hasn’t always been the case,” he added, in a reference to Trump.

But Biden has yet to deliver on his own commitments as coal-state U.S. Sen. Joe Manchin has again threatened Biden’s domestic effort. For all the optimism Biden has been radiating at the summit in Scotland, persistent doubts lurk about whether he can deliver solely through executive actions as continued talks with Congress have steadily cut into his ambitions.

Manchin said Monday, at an unfortunate time for the president, that he remained undecided on Biden’s $1.75 trillion domestic policy proposal, which includes $555 billion in provisions to combat climate change.

Manchin holds a key vote in the Senate, where Biden has the slimmest of Democratic majorities, and has successively killed off key parts of the administration’s climate proposals. He said Monday he was uncertain about the legislation’s impact on the economy and federal debt and was as “open to voting against” it as for it.

Biden minimized Manchin’s objections on Tuesday, saying of the senator, “He will vote for this” and “I believe that Joe will be there.”

Biden has essentially bet that the right mix of policies on climate change and the economy are not only good for the country but will help Democrats politically. But questions remain about whether he has enough political capital at home to fully honor his promises to world leaders about shifting the U.S. toward renewable energy.

Gubernatorial elections Tuesday in Virginia and New Jersey — states Biden won in last year’s election — will provide the first ballot-box test of how Americans view his presidency.

Biden joined other leaders Tuesday for an initiative to promote safeguarding the world’s forests, which pull vast amounts of carbon pollution from the air. As part of a broader international effort, the administration is attempting to halt natural forest loss by 2030 and intends to dedicate up to $9 billion of climate funding to the issue, pending congressional approval.

“Forests have the potential to reduce – reduce – carbon globally by more than one third,” Biden said.

The president and European Commission President Ursula von der Leyen co-hosted an event to promote an alternative to China’s infrastructure financing programs. Biden compared his “Build Back Better World” policies to the Chinese programs, saying his would not expose countries seeking infrastructure funds to “debt traps and corruption.”

He then highlighted the commitments by roughly 100 countries to cut methane emissions by 30% over the next decade.

Biden also joined world leaders in promoting investments in new technology to fight climate change and build a carbon-neutral future. “Our current technology alone won’t get us where we need to be,” he said, “We need to invest in breakthroughs.”

The president also met behind closed doors with Prince Charles and “commended the Royal Family for its dedication to climate issues,” the White House said.

Crucial for his time in Scotland is that he’s emphasizing several policies that can be achieved without congressional buy-in, such as the methane pledges and private partnerships.

Back home, his administration chose Tuesday to launch a wide-ranging plan to reduce methane emissions, targeting a potent greenhouse gas that contributes significantly to global warming.

Biden came to the summit saying he hoped to see his legislation pass this week, but Manchin’s new objections threaten to close the narrow window Biden may have to win passage of his initiatives. The senator is eager to preserve his state’s declining coal industry despite coal’s falling competitiveness in U.S. energy markets.

If Biden’s climate legislation falters, he could be limited to regulatory projects on climate that could easily be overturned by the next U.S. president, and turn his stirring cries for climate action abroad into wistful talk at home.

Manchin’s statements are a possible sign that one of two key Democratic votes in the Senate wants to delay votes on the president’s agenda until the bill is fully reviewed. But House Democrats are still taking steps this week to pass Biden’s $1 trillion infrastructure package, which includes efforts to address climate change. The White House is seeking to turn both measures into law, linking them in hopes of appeasing a diverse and at times fractious Democratic caucus.

White House press secretary Jen Psaki pushed back, saying the administration is confident the spending package already meets the criteria set by Manchin.

“It is fully paid for, will reduce the deficit, and brings down costs for health care, childcare, elder care, and housing,” Psaki said. “We remain confident that the plan will gain Senator Manchin’s support.”

Associated Press writer Matthew Daly in Washington contributed to this report.