When he's not going mental on Twitter, President Trump is playing a pretty strong hand in China.

On Sunday, a U.S. Navy destroyer, Stethem (named after Robert Stethem, a sailor who was murdered during a 1985 hijacking by the Lebanese Hezbollah), sailed within 12 nautical miles of the Chinese-claimed Triton Island. Located in the Paracel chain, Triton is around 190 miles from Vietnam and 150 miles from China's Hainan island.

Yet with territorial waters extending only 12 miles offshore, neither nation has grounds for a unilateral claim.

Still, China believes it owns the entire region of these waters. In the chart below, I have drawn lines of claims to the Paracel and Spratly islands, from China, Vietnam, and the Philippines. Considering the distance between China and the Spratly islands, in particular, it is clear China's claims are absurd. The Spratly islands are 560 miles from China, but 85 miles from the Philippines.

Of course, China doesn't see it this way. And in light of the Stethem's operation, they are threatening escalation. A spokesman promised that "The Chinese army will strengthen its defense capacity, increase the intensity of its sea and air patrols, and firmly defend national sovereignty and security, according to the extent of the threat that its national security is facing."

Such bluster speaks to something.

As I noted recently, China thinks it holds all the cards. It knows the U.S. is desperate to restrain North Korea's ballistic missile program and in return for significantly pressuring North Korea, China wants Trump to accept China's imperial island dominion. It's important that the U.S. not sign up to this arrangement. Doing so would collapse the international understanding that one nation does not have the right to claim vast fishery, oil, and gas reserves in international waters.

Fortunately, thus far, Trump is applying the right double-edged strategy. He is escalating against North Korea and enforcing China's understanding that he will take action if necessary. At the same time, he is ignoring China's island claims.

It's the right approach for two reasons. First, it pressures China on North Korea. China is deeply concerned by the prospect of a Korean conflict. It knows that millions of refugees would flood across its southern border. Moreover, it knows that the U.S. would be the ultimate victor: and that a pro-U.S. government would take charge over the entirety of the peninsula.

Second, it challenges China's island aggression with reciprocal resolve. The Chinese are powerful, but they know that the U.S. Military would inflict severe losses on their forces in the event of a conflict in the South and East China seas. By ignoring China's threats, Trump is taking the opposite approach to President Barack Obama. During the previous U.S. administration, freedom of navigation exercises were few and far between, and always hesitant.

Trump gave China the chance to seriously pressure North Korea before escalating freedom of navigation operations. They failed to do so, and now they are paying the price.

Ultimately, Trump's policy here is an exercise in realism. Neither weak nor overtly aggressive, U.S. policy towards China is now targeted at a maintained balance of power. A balance that accepts China's power but imposes limits upon its aggressive practice.