TAIPEI, Taiwan >> A former U.S. national security adviser called for deeper interaction between his country and Taiwan during a visit today to the self-ruled island, which has seen increasing military threats from China.

John Bolton, a potential Republican presidential candidate in 2024, said at a pro-Taiwan independence event in Taipei that national security teams from both sides must develop contingency plans on how to respond to actions Beijing might take, warning it would be too late once an attack occurs.

“And we have to tell China and Russia what the consequences are if they take actions against Taiwan. Not just in the immediate response, but over the longer term, to basically excommunicate China from the international economic system if it did take military actions against Taiwan or attempt to throw a blockade around it,” Bolton said.

Bolton, former President Donald Trump’s hawkish national security adviser, started his week-long trip to Taiwan on Wednesday. The visit reflects the importance of the island’s democracy as an issue in the U.S. presidential election next year amid heightened tensions between Washington and Beijing.

Taiwan and China split in 1949 following a civil war that ended with the Communist Party in control of the mainland. The island has never been part of the People’s Republic of China, but Beijing says it must unite with the mainland, by force if necessary.

The U.S. remains Taiwan’s closest military and political ally, despite the lack of formal diplomatic ties between them. U.S. law requires Washington to treat all threats to the island as matters of “grave concern,” though it remains ambiguous over whether American forces would be dispatched to help defend the island.

Bolton said the backlog of U.S. military sales to Taiwan is estimated to be $19 billion and it needs to be resolved.

“Part of that is a U.S. problem. Our defense industrial base is not as strong as it used to be. We need to improve that for global reasons, but particularly for Taiwan,” he said.

On Friday, the Taiwanese Defense Ministry said China’s military flew 38 fighter jets and other warplanes near Taiwan. That was the biggest such flight display since the large military exercise in which it simulated sealing off the island after the sensitive April 5 meeting between Taiwan President Tsai Ing-wen and U.S. House Speaker Kevin McCarthy. China opposes any exchanges at the official level between Taiwan and other governments.

Later Friday, China’s People’s Liberation Army also issued a protest over the flight of a United States Navy P-8A Poseidon anti-submarine patrol aircraft through the Taiwan Strait, calling it a provocation that the U.S. “openly hyped up.” But the U.S. 7th Fleet said Thursday’s flight was in accordance with international law and “demonstrates the United States’ commitment to a free and open Indo-Pacific.”

Bolton is scheduled to join a banquet on Monday organized by the Formosan Association for Public Affairs, a pro-independence organization headquartered in Washington, D.C. Tsai will also attend the event.