Its because for decades the United States has been one of the chief mediators in the peace process, and by making this move it essentially delegitimizes the US’s role as an impartial arbiter in conflict.

这是因为几十年来，美国一直是和平进程的主要调解人之一，此举实质上削弱了美国作为冲突中公正仲裁者的作用。