If you want to know why sanctions haven't stopped Kim Jong Un, look no further than the northeastern Chinese city of Dandong.

It's the site of the bustling China-North Korea Friendship Bridge, which links Dandong and the North Korean city of Sinuiju, a place Kim's father, Kim Jong Il, designated a special administrative region in 2002 as part of market-economy experiments. Fourteen years on, its rail and truck traffic is a metaphor for why neither Washington, nor Seoul nor the United Nations has brought the Kim dynasty to heel. And it's where Donald Trump should look if he wants to take a hard line on China without killing the global economy.

President-elect Trump's promised Chinese trade war — with tariffs as high as 45 percent — would be a pyrrhic victory, slamming global growth and boosting living costs. Here's a better idea: wage a commercial war instead by sanctioning Chinese companies that keep the Kims in business. It would simultaneously get Xi Jinping's attention and chasten the world's most dangerous regime.