There's a general tendency to vote the "not that one" way and 4 years ago being specifically not-Hillary probably helped Trump a lot.
But regardless of who exactly is his opponent in a given election, Trump is (appears to them as) not business-as-usual, not a product carefully crafted by PR agencies and decades in politics. The post Cold War era produced a political consensus that made parties converge to the center and politicians became near indistinguishable big tent, something little for everyone drones and people got tired and wanted something else. Something with any illusion of substance instead of the amorphous nothing. Obama tapped into that too, although in a different manner. Trump by saying outrageous things and generally not playing by the rules was different from the amorphous nothing, therefore he became the desired "something".
But regardless of who exactly is his opponent in a given election, Trump is (appears to them as) not business-as-usual, not a product carefully crafted by PR agencies and decades in politics. The post Cold War era produced a political consensus that made parties converge to the center and politicians became near indistinguishable big tent, something little for everyone drones and people got tired and wanted something else. Something with any illusion of substance instead of the amorphous nothing. Obama tapped into that too, although in a different manner. Trump by saying outrageous things and generally not playing by the rules was different from the amorphous nothing, therefore he became the desired "something".