I won't deny Obama is the one who inspired him to become president -- that correspondents dinner was absolutely the catalyst -- but Donald Trump never ran and lost against Obama. You think the temper tantrums he throws over Biden or Obama now are bad, I cannot fathom the temper tantrum he would've had if he lost to a black man (let alone the one we would've, could've, should've gotten to see if he lost to a black woman).
But the one thing Trump hates more than anything, more than every racist, sexist, -phobic prejudice he has, is losing to people. He views every interaction as a competition (look at the way he shakes hands, he has always done that), and the more public, the more humiliating the loss, the worse of a tantrum he throws over it. Look how hard he pissed and moaned all throughout Biden's term. Look how hard he's fought to not pay E. Jean Carroll (it's not about the money, he can afford it; and it's not about the reputation of being a rapist, he knows his reputation is garbage outside of his base). Think of how much time he spends playing golf and ""winning"" tournaments at his own golf courses. Losing, at anything, is the one thing that really, truly gets under his skin. And to Biden he lost the most public kind of competition a man can lose.