After being recalled to Yan'an, Peng was subjected to a political indoctrination campaign in which he was criticized as an "empiricist" for his good relations with the Comintern and survived professionally only through an unconditional conversion to Mao's leadership. Mao ordered Peng to be criticized for 40 days for the "failings" of the Hundred Regiments Campaign (even though Mao had supported it and later praised its successes). Peng was not allowed to reply and was forced to make a self-criticism. Privately, Peng resented Mao's criticism of him, and in 1959 once told Mao: "At Yan'an, you fucked my mother for forty days."