And they continue to support North Korea:https://www.infowars.com/china-warns-trump-we-will-back-north-korea-if-the-us-strikes-first/
Here is a simple idea: if and when North Korea launches an effective nuclear attack on the US mainland, we consider it an act of war by China itself, and react accordingly.
Obviously, a nuclear war is not the outcome we want, but it is not the outcome they want either. But given that China can shut them down any time they want, they are CLEARLY culpable.
If we add this to the table, along with the threat of a tiered trade war we can escalate gradually, perhaps they can be made to see reason.
China itself is not peaceful, and its leaders not secure in their power. They are corrupt, greedy, brutal, and indifferent to anything not directly related to an unearned national pride, or the internal violence needed to keep hundreds of millions of miserable people from committing mass slaughter of the dictators who call themselves liberators.
It is very possible to put real pressure on both these nations, or so it seems to me.