He was Marco Rubio’s roommate, the “Robin” to his “Batman,” and he was as hardline an anti-Castro, socialist-hating politician as you’d find in South Florida—which is saying something. That’s until former Republican congressman David Rivera signed a $50 million contract with the US subsidiary of Venezuela’s state oil company.

Federal prosecutors allege that Rivera was at the center of a covert scheme aimed at convincing the first Trump administration to ease its sanctions on the Nicolás Maduro regime and get the oil giant ExxonMobil operating in Venezuela again. (Rivera pleaded not guilty to the charges and has denied any wrongdoing.) Also allegedly tied to the purported scheme: a Miami real-estate developer previously convicted of being a Cali cartel cocaine dealer, a Venezuelan media mogul who wanted his pro-Maduro propaganda channel on US screens, and Delcy Rodriguez, the acting president of Venezuela after US forces kidnapped her boss and left her in charge.

Rivera was eventually indicted for acting as an unregistered foreign agent for Caracas, as well as on conspiracy, money laundering, and tax evasion charges. The feds seized $24 million and five properties from Rivera and an alleged associate. The first of his two criminal trials is slated to begin later this month—and everyone from White House chief of staff Susie Wiles to former Trump campaign manager Kellyanne Conway to GOP representative Pete Sessions to Trumpland’s favorite lobbyist Brian Ballard has been dragged into the years-long proceedings. And there’s one very big name on the witness list: Marco Rubio.

Rivera and Rubio came up in politics in the ’90s as a team. Rubio was the golden child, Rivera the “feared” and “consummate behind-the-scenes strategist,” as one Rubio biographer put it. Both were sons of Cuban immigrants. Both were clear in their desire to bring down the dictators in Havana and Caracas, although Rivera was the only one who smeared his rivals as “business partners with the regime.” He was also accused of slamming into a truck carrying his opponent’s campaign fliers, though no charges were filed. (Rivera said he was trying to pull the truck over.) The two were close enough that they bought a house together when they were state legislators. That proximity became a headache for Rubio when they both ran for higher office.