We deal openly with the ChiComs, and we fought them to a standstill in the early 1950's. Many Americans dead as a result.

From what I have read and heard, Vietnam is far ahead of actually being friendly towards us than the ChiComs, and our conflict with them is more fresh than the one with their northern neighbor. Also, an enemy of my enemy is my friend (like it or not) does indeed play into our foreign relations scheme.