Mr. Trump’s initial reluctance to confront China’s territorial claims once he became president came despite his criticism during the campaign of the Obama administration’s handling of the issue. In an interview with The New York Times in March 2016, Mr. Trump said that Beijing had built in the South China Sea “a military fortress, the likes of which perhaps the world has not seen.”
The naval operation on Wednesday was being interpreted as a welcome sign of American engagement in the South China Sea by allies of the United States in the region.
Even so, Australia, whose economy is highly dependent on exports to China, has declined to participate in the United States-led military operations, arguing that China now controls the Spratly Islands, where Beijing has placed military weapons and runways for fighter jets.
“Australia is extremely reluctant to participate in freedom of navigation operations that involve flying over or sailing through the 12 nautical miles around the islands,” said Alan Dupont, a former Australian defense intelligence official.
“The Australian government feels it would be provocative and upset China,” Mr. Dupont said. “It feels it would be counterproductive now that China has militarized the islands.”
Allies would be watching to see how consistent the Trump administration would be on the South China Sea, some analysts said.
“One operation won’t ally fears about Trump’s transactional approach toward China and its apparent disinterest in defending international and legal rights,” said Euan Graham, an analyst with the Lowy Institute in Australia.