As President Trump was locked in a war of words with the leader of Colombia over the military deportation of migrants, China’s ambassador to Colombia declared that relations between Beijing and Bogotá were at their “best moment” in decades.

Zhu Jingyang, the ambassador, later said that it was a coincidence that he posted his comment on social media last week, a day after Mr. Trump said he would slap tariffs on Colombia. But the public outreach suggested that Beijing saw an opportunity to strengthen its hand in the high-stakes superpower rivalry between China and the United States.

Two weeks into the second Trump administration, Mr. Trump’s aggressive “America First” foreign policy holds both promise and peril for Beijing.

The perils have always been clear: more tariffs, and the risk of a wider trade war. This weekend, Mr. Trump imposed an additional 10 percent tariffs on goods imported from China, saying the tariffs were a response to China’s failure to curb fentanyl exports. He could answer any retaliation from China with even higher levies.

But even as Beijing calculates the impact of the tariffs on China’s weak economy, it is surely also taking stock of the openings that Mr. Trump’s other moves are giving China.

Mr. Trump has alienated U.S. allies and partners like Canada and Mexico by imposing steep tariffs on their exports. He has weakened America’s global authority by cutting foreign aid and withdrawing from the World Health Organization and the Paris Agreement, a U.N. climate pact.