Former President Donald Trump has had a massive flaw ever since he was a kid, that has been one of his greatest weaknesses, said his niece Mary Trump in a recent TikTok video. The younger Trump, a psychologist by trade, has been a frequent critic of her uncle, and has often sought to unpack his mental abnormalities that she says are responsible for his behavior in life and politics. “Even as a little kid, he was incapable of having a sense of humor about himself, which is really not great. Kids need to have that kind of resilience that he never had,” she said in the video. “But worse, at seven…