I suspect that when Putin talked in Uzbekistan about China's concerns a few days ago it was about nuclear weapons and that he'd given them private assurances that any public threats were no more than words.China will have their own red lines, and I suspect the use of nuclear weapons in any capacity goes way beyond it. China is a big fan of order and stability in the world, and while they enjoy toying with the US (hence their tightly leashed poodle in Pyongyang) they won’t have any interest in upsetting the apple cart permanently. Nuclear weaponry brings the potential for huge, unpredictable consequences and that will be well outside Beijing’s risk appetite. China also knows they’re now the dominant partner, Russia needs China now more than China needs them, and as such Moscow will have to stay in line. Because if Putin goes rogue, even if those around him in the Kremlin don’t take steps to remove the evil house elf, somebody from the Chinese security services will be more than ready to.