MEXICO CITY—The grainy video looks like something from a surveillance camera. Two men sit at a booth in a restaurant in southern Mexico. One man calmly slides a paper bag full of cash across the table to a man sitting across from him. Both keep talking, as if nothing has happened.
The video would be unremarkable if one of the men weren’t Pío López Obrador, the younger brother of Mexico’s president, Andrés Manuel López Obrador, a leftist nationalist who has framed his political career as a crusade to end endemic corruption.
The emergence of the video last month is the latest challenge to Mr. López Obrador’s effort to cast himself as a corruption fighter. During his first two years in office, he has ignored calls to strengthen a national anticorruption system created under his predecessor. He has faced questions over the real-estate holdings of one of his cabinet members, and anticorruption activists say he appears more interested in using high-profile prosecutions to score political points against rival politicians.
The video is one of two, which were published earlier on Mexican news website Latinus, that allegedly show the president’s brother receiving a total of 1.4 million pesos (equivalent to about $94,000 at the time) in bags of cash on two separate occasions in 2015. In the videos, the men discuss the amounts changing hands.
The president has said the videos are authentic and has defended his brother, saying the money came from ordinary people and was used for campaign expenses like buying gasoline. But he said he doesn’t know whether the campaign contributions were legal and has called for investigations by the attorney general’s office and Mexico’s electoral agency, which has opened an inquiry.