But the "America first" approach has also left the United States far more isolated. The overall impact of the policy, say diplomats, politicians and analysts interviewed around the world, has been a clear retrenchment of U.S. power — and an opportunity for U.S. adversaries such as China and Russia.
The American role in the world has been diminishing for years as other countries have expanded their economies, militaries and ambitions.
Foreign-policy players, however, say they see something different now: A disorderly U.S. transformation from a global leader working with partners to try to shape the world to an inwardly focused superpower that defines its international role more narrowly. The Trump administration has emphasized counterterrorism and American economic advantage in its foreign policy, while downgrading such traditional U.S. priorities as promoting human rights, democracy and international development.
Trump's approach has won praise from countries including Israel and Saudi Arabia but is strikingly unpopular in many nations: A Gallup survey of attitudes in 134 countries that was released Thursday showed a significant drop in support for U.S. leadership in the world, from a median of nearly half of people approving under President Barack Obama to fewer than a third doing so under Trump.
"What he has achieved is a remarkable weakening of America's moral standing," said Norbert Röttgen, chair of the German Parliament's foreign relations committee and an ally of Chancellor Angela Merkel. " 'America first' has made America weaker in the world."
The White House did not respond to a detailed request for comment.
Across the globe, U.S. adversaries are rushing to fill the America-size void left as Washington breaks from its closest allies on trade and other international pacts. They also seek to take advantage of the confusion caused by what allies and foes have called an ill-defined and sometimes chaotic U.S. foreign policy broadcast by Trump's tweets.
"There's a vacuum now," said a U.S. official who works on Middle East issues and who, like others interviewed for this story, spoke on the condition of anonymity to comment freely. "And you're going to have some try to step in."
At a World Trade Organization meeting last month in Buenos Aires, that someone was China.
The meeting, a biennial affair, usually delivers bromides about the advantages of global commerce along with some tweaks to the system. This time, though, U.S. Trade Representative Robert E. Lighthizer delivered a combative speech, accusing members of unfairly taking advantage of the group's rules — an echo of the president's oft-repeated denunciation of "dumb trade deals."
Allies said they got the message: The United States was not there to find common ground.
"The whole U.S. delegation, not only Lighthizer, at all meetings and bilaterals, made clear in a very explicit way no joint declaration or a common work program could be agreed from the U.S. side," said a European official involved in the negotiations.
Attendees watched as Chinese officials advocated more forcefully for free trade — and then worked the sidelines to seek deals with other nations, according to a senior European official who was at the meeting.
"You see them active everywhere," the official said, adding that the buzz of Chinese activity was clear from the scores of meeting rooms the Chinese delegation booked.
In a statement, Lighthizer said that he was ready to make worthwhile deals but that poor agreements weaken the global trading system.
"It is fatuous for the Europeans to blame the United States for the failure of the WTO to arrive at negotiated outcomes in Buenos Aires," Lighthizer said. "The E.U. approach — which is to agree to a deal simply for the sake of doing so — is antithetical to the global trading system. And to be clear, China got nothing from the ministerial."
Trade is not the only area in which China has seen opportunity. The emerging superpower also has benefited from a storm of acrimony in recent weeks between Washington and Pakistan, a nuclear-armed nation that has long had a tense partnership with the United States.
As Trump has tweeted about the "lies and deceit" of the Pakistani government and his administration suspended nearly $2 billion in military aid, China has gleefully stepped in to offer support. In recent years, the Chinese have committed to a $62 billion infrastructure plan in the region. Pakistan has taken pains to differentiate between the two powers.
"China is a strategic partner, while the ties with Washington are tactical," said Mushahid Hussain Sayed, chairman of the defense committee in the Pakistani Senate.
Many diplomats and policymakers say they think Washington will remain the preeminent global power but with greatly dimmed ambitions — even after Trump's tenure in the White House.
"The U.S. is not the reinsurance company for the global order. It's no longer the guarantor of last resort," said Reinhard Bütikofer, a German member of the European Parliament who works on transatlantic issues. "If the beacon on the hill doesn't shine anymore, that has an impact."
The impact can be seen in the fact that even longtime U.S. allies such as India, Turkey and Latin American nations are casting about elsewhere for dependable friends. Indian leaders have worked to deepen strategic relationships with Japan, Australia, Israel and other countries. Mexico, meanwhile, has accelerated free-trade talks with Argentina, Brazil and Europe.
Trump's victory threw Mexico into a near state of emergency. Several key Trump goals — building a wall along the U.S.-Mexico border, deporting more illegal immigrants and radically altering the North American Free Trade Agreement, or NAFTA — could pose acute threats to Mexico's economy.
The country's worst fears have not been realized, but avoiding a crisis takes constant effort.
"A bloody roller coaster," in the words of a Mexican official, "trying to read between the lines, between the tweets, between the different messages coming from whomever you spoke to last, including the president himself, then trying to decide what to make out of it."
Röttgen said that Trump was so unpredictable that some European leaders had become more cautious about seeking to meet with him.
"It's open to accidents. It's unpredictable. It's always seen from a transactional viewpoint," he said.
A top adviser to one European leader said they no longer try to schedule time with Trump on the sidelines of summits. "Always, you're looking for a chance to meet up with the U.S. president," the adviser said. But now, that leader communicates via lower-level, less volatile U.S. officials, the adviser said.
Still, most of Washington's closest European allies continue to seek discussions with the president. Norway's prime minister visited the White House this month. French President Emmanuel Macron is seeking a meeting with Trump at the World Economic Forum in Davos, Switzerland, this week, if the federal government shutdown doesn't prevent him from making the trip. And leaders who once fretted that Trump would abandon some of Washington's core international commitments are now reassured by robust U.S. troop deployments across Europe.
But even those who enthusiastically embraced the Trump administration have been nonplused by the president's style and decisions.
Early in Trump's tenure, for example, Egyptian officials sensed they finally had a U.S. president who understood them. The Obama administration had been reviled by the government of President Abdel Fatah al-Sissi for its focus on human rights and democracy.
But Trump's tweets and confusing U.S. policy moves have proved frustrating — and alienating. By August, Egyptians were fuming after the U.S. government, citing human rights concerns, cut or delayed nearly $300 million in assistance. Then came the decision to recognize Jerusalem as Israel's capital and relocate the U.S. Embassy there from Tel Aviv.
"Now we have a situation where the words are not enough," said the U.S. official who works on Middle East issues. "In the early days of the administration, the words meant something. President Trump's praise of Sissi meant something. Now, between the August decision and the Jerusalem decision, they have lost faith."
Trump's policies still win praise in some quarters. Saudi officials enthusiastically greeted him in a May visit, delighted that Trump had rejected Obama-era policies that were less hawkish toward Iran. And in Israel, views of the United States have markedly improved under Trump, who has been far more supportive of the right-wing government of Prime Minister Benjamin Netanyahu than Obama was.
Trump "has brought fresh thinking to the White House," said Israeli Deputy Foreign Minister Tzipi Hotovely. "He understands the region better than those experts who warned that if he recognizes Jerusalem as Israel's capital or moves the embassy to Jerusalem, the Middle East will explode. It did not explode."
But prospects for an Israeli-Palestinian peace deal, already dim, have evaporated.
"There won't be peace — no negotiations, no normalization, and the Middle East will be sitting on a volcano" until the decision is reversed, said Nabil Abu Rudeineh, a spokesman for Palestinian Authority President Mahmoud Abbas.
The Trump administration has escalated the U.S. offensive against Islamist insurgents in places including Somalia and Afghanistan, and given American military commanders more latitude in decision-making as they fought the Islamic State extremist group in Iraq.
In Somalia, the U.S. military carried out at least 34 airstrikes in 2017 compared with roughly 14 in 2016. But some officials at the State Department have raised questions about the amplified Pentagon role. There has not been a proportionate increase in diplomatic activity in Somalia. Instead, the size of the U.S. diplomatic mission has shrunk, and the U.S. ambassadorship there has not been filled.
Airstrikes and other military action can have knock-on effects that politically savvy experts could help avert, but "because the department's footprint is so limited compared to the military engagement, diplomats lack the bandwidth," said a former State Department official.
A similar dynamic is at play in Afghanistan.
At a ceremony in Kandahar in November to showcase refurbished Black Hawk helicopters being provided to the Afghan government, the top U.S. military commander, Army Gen. John W. Nicholson Jr., gave an upbeat speech about defeating Taliban insurgents.
But off to one side, a group of invited local elders, clad in turbans and robes, conferred in worried whispers over an entirely different issue.
"We must speak to him about the elections. Everyone is very worried," one elder said.
As soon as Nicholson and his interpreter had sat down, the group bombarded him with concerns, saying that the plans for national elections in July were being undermined by political pressures, ethnic bias and other problems. If the Americans did not intervene, they warned him, the elections could turn into a disaster.
Nicholson smiled and promised to pass on their concerns. But the general's mandate does not include politics, and there has been far less diplomatic focus on Afghanistan than was the case under Obama. The country was without a U.S. ambassador until last month, and a special U.S. envoy post has been scrubbed.
Over the past year, some U.S. allies have said they worried about being kept in the dark as the U.S. government developed its plans for military action. A delegation of senior E.U. ambassadors responsible for security policy for the 28-nation group traveled to Washington in late June and sought details from U.S. officials about the new administration's foreign policy. One said he returned to Europe "in despair."
The diplomat said he received no useful guidance about the administration's strategy in Iran, Syria or Afghanistan — or, crucially, about how to interpret the president's increasingly belligerent tweets aimed at North Korean leader Kim Jong Un.
The war of words between Washington and Pyongyang dominates a long list of apprehensions for U.S. allies for 2018 but is seen as an opportunity for others.
In response to Trump's volatile brand of dealmaking and brinkmanship, Moscow has sought to present itself as a trustworthy interlocutor.
Russian Foreign Minister Sergei Lavrov said in September that Moscow was ready to mediate the dispute between Trump and Kim, which he likened to a "kindergarten fight."
Some officials have noted the irony of Russia and China presenting themselves as guarantors of stability and global free trade.
When the Trump administration last January pulled out of negotiations over a 12-nation trade pact, the Trans-Pacific Partnership, 11 would-be members of the pact were left to work out the details without U.S. input. The deal had long been seen as an alternative to a Chinese regional economic order.
The U.S. exit gave Chinese President Xi Jinping, the authoritarian leader of one of the world's most tightly controlled economies, the chance to present himself as a champion of globalization.
The Chinese "haven't had to spend any energy to emerge much more clearly as the global leader that they aspire to be," said David Rank, who resigned as acting U.S. ambassador to China over the administration's decision to pull out of the Paris climate accord.
Meanwhile, Rank said, U.S. influence is ebbing.
"For my entire career except for the last four days of it, the question in foreign capitals, was 'What does Washington think about this?' " Rank said. "I suspect that is not the case anymore."
Birnbaum reported from Brussels and Paris. Anna Fifield in Tokyo, Emily Rauhala and Simon Denyer in Beijing, Pamela Constable in Kandahar, Kevin Sieff in Nairobi, Quentin Ariès in Brussels, Annie Gowen in New Delhi, Shaiq Hussain in Islamabad, Loveday Morris and Ruth Eglash in Jerusalem, Joshua Partlow in Mexico City, Sudarsan Raghavan in Cairo, Anton Troianovski in Berlin, Andrew Roth in Moscow, and David Lynch and Anne Gearan in Washington contributed to this report.