Republican presidential candidate Donald Trump wants to withdraw American forces from Asia and let allies Japan and South Korea defend themselves. He suggests that these two Asian powers might best develop their own nuclear weapons.

Like most American foreign-policy scholars, I think these ideas are fundamentally unsound. They would increase the risk of war between Japan and China in particular, especially during any transition period. They would also greatly weaken the Nuclear Non-Proliferation Treaty, under which nonnuclear countries agree not to pursue the bomb.

But the biggest danger from Trump’s ideas on Asia is the risk of war in the Taiwan Strait. Absent bases in Japan, the U.S. cannot realistically deter Chinese military attacks on Taiwan. This reality could lead China to contemplate the use of force with much less hesitation than it has shown to date.

Knowing this, leaders in Taiwan might seek to develop nuclear weapons of their own as a deterrent. But China has repeatedly stated over the years that Taiwan’s pursuit of the bomb could lead to the very Chinese attack it was designed to prevent.

It is important to review the basics. Since the late 1970s, when the U.S. switched its formal diplomatic recognition to mainland China, it has not treated Taiwan as an independent country. But under the 1979 Taiwan Relations Act, Washington is committed to help Taiwan defend itself against any forceful attempt at reunification by mainland China. The law obligates the U.S., among other things, to consider providing weaponry to Taiwan, and to consider the use of American military power in a conflict.