What a strange analysis. You think that the determinant of whether or not the USA is a world power is who is elected to a 4-year term? The USA still has 600+ military bases in 80+ countries, still has the world reserve currency, still has the influence over OPEC that requires it to trade oil in USD, still has ever world leader seriously considering their every word and deed through the lens of American hegemony.

What exactly about this election suddenly made America not a world power?

The vote was a response to falling global power to begin with. Trump can’t stop it, but he didn’t start the process either.