Well, I admit that inviting the president of the Russian Federation to the US under false pretenses to assassinate him would increase the chance of every state on Earth being destroyed all at once. It would certainly be an act of war. Even if there were no nuclear exchange in the immediate aftermath it would then be established that every diplomat to US territory was also a hostage at best or being sent directly to their death at worst. It would further kick out the bottom rungs of the escalation ladder for future conflicts.