First: USA is only one that has known as superpower country in the world refers to Francisco Fukuyama hipotesa (The End of History and The Last Man), it forces us to have to give more attention to the result of its election because every single policy that proposed by USA government will affect the international politics which directly influence the domestic politics to each country. The evidence from this, take a look at the case of increasing tariff to China Products, actually that is the domestic regulation that was done by Trump but somehow this regulation caused Trade War to both countries and affected to others countries.
Second: The President of USA is President of The World, this statement refers to Ahmad Sahide’ argumentation which can be found on his book “Gejolak Politik Timur Tengah” that said foreign policy of USA determined world politics. Early on this year (2020), under Donald Trump’ administration which declared that by killing Qasem Soleimani is one of the way to bring peace in middle east, however this caused international politics interpreters assumed that the world is going to face the third world. And moreover when Trump recognized Jerusalem as the Capital city of Israel trough this policy in igniting conflict between two countries.
Actually, there several argumentations that can be categorized as a evidence to make the result of USA presidential election is so important, but here these two arguments are stronger that we can see.