It is time to stop debating the wisdom or competence of President-elect Donald Trump’s call with Taiwanese leader Tsai Ing-wen, and start preparing for what China’s coming response might be.

Those who supported Trump’s conversation with Tsai, the first official call between an American President or President-elect since 1979, have pointed to Beijing’s restrained reaction as a sign the move adroitly put China on the defensive, perhaps for the first time. Others have called it a rash and provocative move, possibly one not particularly thought out by the President-elect and his small team.

But the reality is that Taiwan is the one, nonnegotiable red line in US-China relations, meaning it would be foolish to think Beijing will sit by and watch how Trump decides to reform US policy toward Taipei, let alone “normalize” it in international society.

Since the “One China” policy was adopted when Washington recognized Beijing, ambiguously claiming there is but one China, and that Taiwan is part of that China, all three sides have danced gingerly around the issue of Taiwan’s de facto autonomy. However, China has never agreed to accept even a hint of actual sovereignty, and has repeatedly asserted its intention to prevent any Taiwanese declaration of independence. It has also not ruled out the use of force.