It is relevant because if china sets out to do that, only countries siding with those nations would be US, Russia, Israeal. And so what the presidents of these nations say on the matter, does matter. In this case, whether you like it or not, the opinion of US president does matter against chian and helps sets the tone of rest of the nations against china does matter too. And considering china released covid-19 before attacking south east nations, islands nearby, yes the other world power nations standing against china is necessary. Maybe trump could be conflict for you but rest of the nations need whatever president US can offer in this situation.