When the new Sri Lankan government came to office, it sought assurances that the port would never again welcome Chinese submarines — of particular concern because they are difficult to detect and often used for intelligence gathering. But Sri Lankan officials had little real control.

Now, the handover of Hambantota to the Chinese has kept alive concerns about possible military use — particularly as China has continued to militarize island holdings around the South China Sea despite earlier pledges not to.

Sri Lankan officials are quick to point out that the agreement explicitly rules out China’s military use of the site. But others also note that Sri Lanka’s government, still heavily indebted to China, could be pressured to allow it.

And, as Mr. de Silva, the state minister for national policies and economic affairs, put it, “Governments can change.”

Now, he and others are watching carefully as Mr. Rajapaksa, China’s preferred partner in Sri Lanka, has been trying to stage a political comeback. The former president’s new opposition party swept municipal elections in February. Presidential elections are coming up next year, and general elections in 2020.

Although Mr. Rajapaksa is barred from running again because of term limits, his brother, Gotabaya Rajapaksa, the former defense secretary, appears to be readying to take the mantle.

“It will be Mahinda Rajapaksa’s call. If he says it’s one of the brothers, that person will have a very strong claim,” said Ajith Nivard Cabraal, the central bank governor under Mr. Rajapaksa’s government, who still advises the family. “Even if he’s no longer the president, as the Constitution is structured, Mahinda will be the main power base.”