First, as a brand new candidate, he took on 15 other Republicans and a hostile news media (go back and watch those debates and note how often the most hostile questions and the greatest expressions of scorn and contempt were aimed at candidate Trump).
As the Republican nominee, he defeated the Hillary Clinton machine and the elite media.
However, these two remarkable achievements were never fully acknowledged because victory on election night was repudiated psychologically. The propaganda media of the left, left-wing activists and Democratic politicians went into hyper aggressiveness to discredit and delegitimize the Trump victory.