The leaders of North and South Korea have met, shaken hands, taken symbolic yet hugely consequential steps across into each other's territory, talked about possible pathways to peace on the peninsula, issued a joint communique, and returned home well satisfied with the breakneck speed of progress thus far. Who deserves the most credit for this outbreak of goodwill induced by the spring of summits?

For U.S. President Donald Trump, an admirer is never further away than a mirror. He is fully convinced of his own negotiating genius and not short of sycophants ready to praise his policy of maximum pressure for putting Pyongyang on the path to denuclearization. The danger of believing his own hype is it might lead him to terminate the Iran nuclear deal, which in turn could end the Korean spring.

Unilateral sanctions by themselves rarely change the behavior of target regimes. Rather, it is the mixed strategy of inducements for good behavior alongside punishment for noncompliance that shifts regimes under international pressure.