U.S. prosecutors filed a straightforward, easy-to-prove criminal case against former Trump campaign manager Paul Manafort, leaving him with a stark choice: cooperate or fight the charges and, if he loses, face years in prison.

The indictment, unsealed on Monday, relies extensively on so-called document charges — essentially that Manafort and his business partner Richard Gates didn't file reports to the government that they were required to under the law. Such cases are rarely prosecuted, but they still carry the potential for prison time, particularly when combined with the more serious charges of money laundering. The maximum sentence for money laundering is 20 years. Cooperation with Special Counsel Robert Mueller, on the other hand, can win Manafort leniency.

"They've adhered to the old adage of, 'Keep it simple.' This is not an over-broad indictment, and I think their goal here is to make it quick," said Peter Henning, a law professor at Wayne State University in Detroit and former federal prosecutor. "It could be a means to gain their cooperation in a broader investigation, and I think that's what Mueller's trying to do."