The twice-impeached president painted a fantasy world in office, starring himself. In this world, he did things bigger, better, more boldly than all who came before him while facing enemies more pernicious than any in creation.
In service of his ego, his nature and his reelection prospects, he said things that were not only wrong, but the precise opposite of right. He said them over and over, in leaps and bounds, and no less so when the deceptions were exposed.
I cannot tell if Trump actually believed what he said or not. The most convincing con man is one that believes his own lies.