I don't think this is much of a mystery, to be honest. Think of the term "loser" for a second. Who do we apply that term to? It's not necessarily people who don't have a lot of material success -- there are plenty of people who don't have much going for them by worldly standards but are nevertheless content. Because they're content, they're not really "losers."
When I think of who we call "losers," what comes to my mind are people who are not content with what they have, and believe they deserve more. Because of ineptitude, they cannot attain whatever measure of status they feel they deserve. Maybe they want to be a fit, attractive person but can't stop binge eating and can't settle in to a workout routine. Maybe they fancy themselves a great businessperson but they can't manage money and get suckered into bad debts. Perhaps they want to be a respected intellectual but they don't have the attention span to earn a degree. If you could tune in to their internal dialog, I think you'd hear someone who believes they already are a winner according to whatever identity they've adopted -- charmer, businessperson, intellectual, etc., and they are in complete denial of the much more limited person they really are.
Trump "tapped in" to white losers. Racism and xenophobia is a drug for them. It provides these losers with an infinite supply of external reasons for their lack of real world results. As a consequence, their denial is trivial to sustain.
Trump is also one of those losers, but in one of the most bizarre twists of fate in human history, the entire Kingdom of Loserdom somehow managed to get him elected into the most powerful position on the planet. He embodies their denial, but magically turned into truth. He's their grandiose delusions made into reality. He is the loser whose wishes for glory came true.