treason already included the death of sons—that if treasonous individuals did not care about their own children, they would not care about their brothers. Emperor Taizong agreed and rejected the proposal to increase the penalty. In 643, in the aftermaths of major conflict between Emperor Taizong's sons Li Chengqian (the Crown Prince) and Li Tai (the Prince of Wei), who was Emperor Taizong's favorite son, causing Li Chengqian to plot to overthrow his father in fear that his father would replace him with Li Tai, Cui submitted a secret petition urging for Li Tai to be made crown prince. Emperor Taizong, after some deliberation, deposed both Li Chengqian and Li Tai, holding Li Tai's machinations responsible for Li Chengqian's downfall, and as Cui had wanted Li Tai made crown prince, he drew Emperor Taizong's ire and was demoted to the post of assistant minister of palace supplies. Later, his post was changed to deputy minister of census. During the preparations for Emperor Taizong's campaign against Goguryeo in 644, Wei Ting () the minister of imperial shrines was made in charge of shipping troop supplies over the Bohai Sea, and Cui assisted him; Cui also had the additional responsibilities of shipping troop supplies in the Henan region. Cui, believing that the supplies from distant prefectures would not arrive in time, took the initiative of requisitioning the food collected as taxes in the region he was in charge and shipping those as food supplies for the troops. However, in spring 645, during the campaign, Wei was accused of not getting supplies to the troops quickly enough and demoted to commoner status. Cui was accused of not paying sufficient attention to the problems of laborers fleeing conscripted labor and was removed from his post. After the end of the Goguryeo campaign, when Emperor Taizong returned from the front to Zhongshan (中山, in modern Baoding), he returned Cui to imperial service, making him an assistant to the head of the legislative bureau of government. He was soon also made acting minister of justice. Later, when Emperor Taizong was to visit his summer palace Cuiwei Palace (), Cui submitted a poem to advise him against doing so in a veiled manner, not wanting Emperor Taizong to be away from Chang'an, and while Emperor Taizong did not accept his veiled advice, he appreciated it. In 648, Cui was made Zhongshu Shilang (), the assistant head of