Taxes

Trump's CFO, Allen Weisselberg, has been indicted for cooking the books, and the DA has pretty solid evidence of this, including the fact that the Trump organization kept two sets of books.

As Chris Hayes points out, the Trump family doesn't seem to be denying that they have done this ... it's just that they're offended by the idea that it's an actionable crime. And it is - many celebrities have ended up in prison for cheating on their taxes, from Al Capone to Pete Rose

The only real question is whether the DA can prove Trump did what he did (what he told Weisselberg to do) with the intent to defraud the government. The fact that he kept two sets of books seems to indicate awareness of guilt.