Few people were suitable to take over the mission.
Those officers who were in charge of the offices could not possibly go to Jiayu Pass since they needed to stay in the capital. Prime Minister Chu could offer some advice, because he did boost the Crown Prince up at Li County a while ago. However, Prime Minister Chu turned down the Gu Family's marital proposal, so it basically meant that he was not supporting the Crown Prince. Therefore, the King could not put Prime Minister Chu in charge.
Among those officers that were in charge of the military… General Liu had the biggest power, and his daughter used to be the Prince Consort of Lord Ling. However, the Prince Consort of Lord Ling stood in opposition to the Crown Prince along with General Liu, who was the most suitable candidate for the mission at Jiayu Pass. So the Crown Prince would need to go to Jiayu Pass to watch over General Liu in case he made a mistake.
Well..
