It was meant to be a moment for the history books — the first time a U.S. president visited a Pacific Island country. Papua New Guinea, the host nation, scrambled to mobilize 1,000 security officers; the leaders of 17 other countries agreed to make the trip for just a few hours with President Biden, who was scheduled to go on to a meeting in Australia with allies known as the Quad.

Now all those plans have been scrapped. The White House announced on Tuesday that Mr. Biden would cut short an Asia-Pacific trip and return to Washington on Sunday after the Group of 7 summit in Japan for debt ceiling negotiations to ensure the United States does not run out of cash and default.

What the cancellation means, in the broadest of terms, is that America’s domestic politics is undermining American foreign policy at a crucial time, in a critical region. Analysts and diplomats warn that fears of an unreliable and dysfunctional America will now be revived in Asia and the Pacific, where the United States has only recently started to build momentum in its efforts to counter Chinese influence.

“It will reinforce lingering doubts about U.S. staying power,” said Hal Brands, a professor of global affairs at Johns Hopkins University. “And you can bet China will make hay of this — its message to countries in the region will be, ‘You can’t count on a country that can’t even perform basic functions of governance.’”

American officials have framed the cancellation as a postponement, arguing that the last-minute change does not reflect a flagging commitment.

“We look forward to finding other ways to engage with Australia, the Quad, Papua New Guinea and the leaders of the Pacific Islands Forum in the coming year,” said a statement from the U.S. Embassy in Australia. The leaders of the Quad nations — the United States, Japan, India and Australia — had planned to meet in Sydney, and Pacific Island leaders in Papua New Guinea.

But for many, the American assurances carried a whiff of déjà vu. President Barack Obama skipped a planned appearance at an Asia-Pacific Economic Cooperation meeting in 2013 to deal with a government shutdown instigated by Republicans. Xi Jinping, the Chinese leader, went on to dominate the event, declaring that “the Asia-Pacific cannot prosper without China.”

Doubts about American resolve — and Mr. Obama’s promise of a pivot to Asia — have been in the air ever since, even as the Biden administration has offered tangible evidence of a shift in priorities. Along with more high-profile visits to the region, the United States has reopened an embassy in the Solomon Islands, added an embassy in Tonga and tilted its foreign policy heavily toward countering China, both militarily and in contested technologies like microchips.

But Washington is still playing catch-up. Beijing’s diplomatic corps worldwide is now bigger than that of the United States, and heavily concentrated in Asia. China has the world’s largest navy and coast guard, and its state-owned companies have surged into the construction and mining industries of many developing countries, including Fiji and Papua New Guinea, which sits just north of Australia.

For much of the region, especially the South Pacific, the United States has yet to prove that it can be as reliably present and productive as China.

“There’s still a sense that this is early days,” said Anna Powles, a senior lecturer in security studies at Massey University in New Zealand. “Trust is the currency of the Pacific, and building trust takes consistency, it takes being reliable, being there, being present.”

Abandoning a meeting of the Quad — which aims to foster collaboration on everything from health care to the environment — may be mostly a logistical irritant. Australia’s prime minister, Anthony Albanese, said on Wednesday that the four Quad leaders would try to meet on the sidelines of the G7 summit in Hiroshima.

Mr. Biden’s aborted stop in Port Moresby, the capital of Papua New Guinea, may carry greater consequences. It is likely to delay or halt efforts to finalize a security agreement that, in early negotiations, involved the possibility of granting the U.S. military unfettered access to the lands and seas around a country that played a strategic role in World War II.

Mr. Biden knows that history intimately: Two of his uncles fought there in the war, and one was killed.

Papua New Guinea’s prime minister, James Marape, said this week that U.S. officials had also promised to deliver billions of dollars in infrastructure investments, and that a group of American executives had planned to join the president’s entourage. It is not clear if or when those pledges will be fulfilled, a costly slight in a poor nation of nine million people desperate for development, where China has already invested heavily in construction and mining.

“There’s no way to deny that this is a big missed opportunity,” said Derek Grossman, a senior defense analyst at the RAND Corporation.

“You can actually argue that going to Papua New Guinea for three hours is more important than going to the G7 or maybe even going to the Quad because it is a new opportunity opening the door to all kinds of possibilities — and now that may be closing because of our own domestic situation.”

For the Pacific Island leaders who had been summoned to Port Moresby to meet with Mr. Biden, there will be additional frustrations. The meeting was billed as a follow-up to their summit at the White House last year, and many had specific requests to address, particularly on climate change, an existential threat to the region.

They had prepared to leave their own domestic politics behind for the gathering, in some cases taking connecting flights to get there. Some, like Fiji’s new prime minister, Sitiveni Rabuka, have said in strong terms that they will work closely only with countries that share their values, distancing themselves from China’s embrace. But many leaders have also expressed annoyance with America’s lack of focus — when, for instance, Secretary of State Antony J. Blinken went to Fiji and talked at length about Ukraine, or when other senior American officials were late for important regional meetings.

Now their attention will shift, back to China, and to another rising power: India.

Prime Minister Narendra Modi, who had planned a visit to Papua New Guinea before Mr. Biden committed and then canceled, will now be the focal point in Port Moresby and in Sydney. Around 20,000 people are expected to gather in Sydney’s Olympic Park for a bilateral celebration on Tuesday.

“Modi is still going to have a state visit in Australia,” said Bates Gill, director of the Center for China Analysis at the Asia Society. “He will be warmly welcomed.”