The 20th time of Romance of the Three Kingdoms, Xu Tianwei attacked Cao Aman. Can you sum up the story of the siege of Xu Tian?

The story of "The Surrounding of Xu Tian" tells that Cao Cao deliberately invited Emperor Xian of Han to hunt in Xu Tian in order to test the attitude of court officials towards him. When Emperor Xiandi was hunting, he missed the deer many times, so he let Cao Cao shoot. Cao Cao directly took the bow and arrow dedicated to the emperor to shoot deer. Uninformed officials and soldiers saw the emperor's special arrow hit the deer and thought it was the emperor, so they cheered long live. Cao Cao stood in front of the emperor and accepted the cheers. The emperor was deeply humiliated, so he called on his ministers to destroy Cao with a belt. Through this incident, Cao Cao also noticed that the emperor's prestige in the hearts of officials and soldiers was still very high, so on the one hand, he stepped up efforts to eradicate the courtiers loyal to the Han Dynasty, on the other hand, he did not dare to replace the emperor immediately.