There wasn't an obsession. Trump just weaponized the word deficit to justify tarrifs. Anyone with an IQ over 100 and two minutes to listen to an explainer video on this would quickly understand the con.
As has been mentioned a couple times in this thread, the trade deficit does have a real negative impact on US industry. Whether or not that's good or bad for a particular person depends on their socioeconomic situation. One would reasonably assume that Trump's base is largely made up of folks for whom the trade deficit has real negative consequences.