Details here. Basically we have some middle-class people (at best!), the Paw family, who live in a tiny house and don't make big money, giving the Clinton campaign a whole lot in campaign contributions. But their contributions very closely track those of a rich fellow named Hsu...who used to live in the home in which the Paws now live. Could Hsu (and possibly the Clinton campaign?) be skirting (read: violating) the campaign finance laws by having several members of the Paw family give money to Senator Clinton's campaign, money that Hsu gave them? If so, that's a violation of the law. As an expert in the article said, there are "red lights" all over this one.
Stay tuned. Note the source of these allegations is the Wall Street Journal news page, regarded by most everyone as a reliable source.