Donald Trump appears to have embarked on a two-track approach to pressuring North Korea into restraining its nuclear weapons and missile programmes. The first track is the ever-tightening economic sanctions that, if properly implemented, could further isolate North Korea from world finance and trade. The second track is a game of chicken to see who can hurl the harshest and most absurd rhetorical insults.

The first track, economic sanctions, took another step forward last Thursday when Trump announced what are potentially the toughest American economic punishments yet, not just going after Pyongyang’s enterprises and people, but also attempting to isolate third parties that do business with North Korea.

This extends beyond the latest sanctions resolution of the United Nations Security Council and could ultimately shrink the grey zone where North Korea has long evaded sanctions. Foreign banks and others that do business with North Korea will face a risk of becoming radioactive in the eyes of the United States, and that may cause them to think twice.

No one should have any illusions, as Andrea Berger pointed out this summer in a report for the Royal United Services Institute: North Korea’s ability to evade sanctions has run ahead of the actual punishments. Reports from China suggest that, while reluctant to sign up with Trump’s broader sanctions regime, Beijing has ordered the agreed-upon financial sanctions against North Korea to be implemented, and China’s Central Bank has demanded no new accounts be opened and older ones be wound up.

The role of China, the chief benefactor of North Korea that is often opaque and ambivalent about the Kim Jong Un regime, can be frustrating and inconclusive. But sanctions and coercive diplomacy, however difficult, offer the best available approach, given the unappealing alternatives. Kim’s dynastic rule emphasises self-reliance and plays off enemies abroad; to change his behaviour will be extremely difficult and take time.

What is harder to grasp about US policy is how such a calibrated pressure campaign fits in with the food fight that Trump escalated with Kim, from the “Rocket Man” sobriquet — “on a suicide mission” — followed by Kim’s reply that the President is a “mentally deranged US dotard”, leading to Trump’s Friday tweet that Kim is “obviously a madman”.

Superheated rhetoric is an old favourite of North Korean propaganda. But what does Trump gain by mucking about in the same gutter? He could simply harden Kim’s resolve and siege mentality.

In New York on Friday, Kim’s foreign minister threatened that Pyongyang may explode a missile carrying a hydrogen bomb over the open Pacific. The danger in such vast threats is the possibility of miscalculation, especially a missile flying, say, over Japan that could not be detected at a critical moment as nuclear or conventional.

Trump ought to focus on making his sanctions work and quit imitating the supposed madman he is trying to pressure.