He took money from a foreigner to donate to political campaigns and tried to influence politicians at the behest of China, without registering as a foreign agent.
He also refused to take a plea agreement that would've spared him most of this (IIUC). They don't like it when a person doesn't "play ball". And it certainly doesn't help that he's Black.
A chinese fraudster who scammed PRC banks that "defected" by claiming to be a dissident, that PRC said for years was a fraudster, who would go on to defraud Americans out of a BILLION dollars, because US state department thought he was some anti CCP dissident with deep insight into the CCP, instead of you know... a fraudster. Though to be fair, both could to be true. I hope US got a billion dollars worth outdated info from him.