During the 2008 Meltdown, China and Russia discussed dumping their Treasuries. Thank goodness they didn't.
China certainly doesn't WANT to dump Treasuries, and it has other levers that it can pull (see rare earths, Nvidia, Boeing restrictions). But yeah, no doubt they'll consider it and bring it up during "negotiations".
ALL of this could have been handled behind closed doors. ALL of it. Instead, Trump just HAD to make a fucking splashy reality TV show out of it, and has destablized both domestic and global markets in the process. Buffoon.