Zhang Xutuo and Wang Sichong enjoyed victories here and there, the situation was deteriorating for the welfare of the Sui state at large. In spring 615, believing in accusations by Yuwen Shu that the official Li Hun () was intending to carry out a coup to replace Emperor Yang with his nephew Li Min (李敏, son-in-law of Emperor Yang's sister Yang Lihua the Princess Leping) and worried about prophecies that someone named Li would become the next emperor, Emperor Yang had Li Hun, Li Min, and their clansmen executed, and further poisoned Yang Lihua's daughter Yuwen Eying (). Later in 615, Emperor Yang carried out a tour of the northern provinces with the Empress Xiao and much of the imperial court. Shibi Khan, angered that the imperial advisor Pei Ju had promised a princess to his brother Ashina Chiji () and had executed his close advisor Shishu Huxi () under false pretenses, launched a surprise attack on Yanmen Commandery. In accordance with Turkish customs, Princess Yicheng had married him as her husband's successor; having been well treated by the empress during an earlier visit, though, she sent a secret warning of his plans to the emperor and his wife. The imperial train sought refuge at the commandery seat in present-day Daixian, Shanxi, which Shibi Khan and his army put under siege on September 11. It was said that Emperor Yang became so fearful that he cried all day long while holding onto his youngest son Yang Gao, the Prince of Zhao. Yuwen Shu suggested that Emperor Yang take the most elite guards and try to fight out of the siege, but Su Wei and Fan Zigai opposed this. Empress Xiao's brother Xiao Yu suggested seeking further help from Princess Yicheng, and Emperor Yang did so. Meanwhile, at Yu Shiji's advice, Emperor Yang also personally visited the soldiers defending the city, raising morale by promising to end the campaigns against Goguryeo and to reward them with honors and treasure. Princess Yicheng falsely informed Shibi Khan that the Turks were under attack from the north and relief troops from Luoyang and the other commanderies began arriving, so the khan lifted the siege. With the danger passed and credit muddled, Emperor Yang followed the advice of Su and Yuwen to renege on most of his promises: he did not return to the capital Chang'an, but went to Luoyang instead; he continued to prepare