Two top aides to Ron Paul’s 2012 presidential campaign knowingly concealed payments to an Iowa lawmaker who agreed to endorse their boss ahead of the state’s first-in-the-nation caucuses, a federal prosecutor said Tuesday at the start of a trial in which the former Texas congressman is set to testify.

“This case is about a cover-up,” said Justice Department attorney Jonathan Kravis during opening statements in the Des Moines trial of Jesse Benton and Dimitri Kesari.