OK. Let's say you're right. They're stalling.
If they're that close, what better time than now rather than when it's too late to yank the Money and support from China rug out from under them?
The majority of the cooperation on nuclear and missile tech has been between NK and Iran. China has a vested interest in keeping the Norks as a buffer between them and western influence. Reported Chinese troop movements near the border can be read a few ways.
1 - Aid for mass refugee influx in the case of war.
2 - Staging area to deal with regime collapse.
3 - A warning for us to stay clear.
Whatever the reason, metal tariffs aren't going to dissuade them. Depending on how far a potential trade war escalates, they may become openly closer. The last thing we need are Chinese personnel coming in as 'invited guests' at key NK installations.