Broadly speaking (for a detailed list see the US Trade Representative's report[1]) they failed to allow access to their markets or respect the rights of foreign companies.

They've shown that a nationalist nation can exploit the globalist system to its own profit, raising doubts about globalism itself and leading to the resurgence of nationalism.

1: https://ustr.gov/sites/default/files/2018-USTR-Report-to-Con...

Promise they made when joining WTO