So far, the US has been unwilling to engage China directly, only using proxy countries to apply pressure, ex. THAAD. It has been highly effective and unless China takes direct action that harms American naval & airforce assets, it's unwilling to engage in a downright skirmish that results in economic loss.
Following that previous logic, China is very careful about not kicking the honet's nest because it would be it's end. The Chinese leadership must know fully well that they cannot match the US militarily. Also given Xi's failing grades on foreign diplomacy, it's suffice to conclude that these grandiose rhetorics are entirely aimed at it's own population, who are reaching a boiling point that will ultimately put into uncertainty the survivability of Xi's powerbase and the entire party itself. Xi made too many enemies so he's looking for ways to survive by fighting fire with fire and creating more enemies from within. An internal dialogue fueling crisis with the US is a perfect propaganda tool and the fear of war, the fear of losing your properties, belongings, material possessions you've spent time on...history has shown is highly effective in controlling the populace.