The problem with US policy at that time is that they see Chaing as both an important ally and a huge liability. After millions of military aids ended up in private bank accounts, the corruption within Chaing's government and army was driving the US nuts. The US was more interested in Mao at that time because they view Mao as less corrupt and a more competent leader than Chaing, and Communism wasn't a serious threat at that time for US.
The corruption of Chaing's government was so bad that most US policy maker believed that Communist victory in the Civil War was caused by the incompetency of the entire Chinese nation in the face of few Soviet agents, and that is it better to cut their losses and wash their hands with China. This stereotype was a huge factor in shaping US opinion that Communist China was only a pawn of Soviet Union, and that China shouldn't even be a factor when Americans entered the Korean War. Of course, this stereotype was completely shattered when China entered the Korean War and demonstrated that there are at least some competent Chinese running around.