Who would most likely agree with this statement?

we must carefully observe and analyze the actions of the Soviet Union to prevent it from spreading communism

That person could be president Harry Truman or any of his close advisors or cabinet officials. The Truman administration adopted and put in practice the doctrine of containment of Soviet communism. The USSR was seen and understood as an expansionist power that wanted to promote communist subversion around the world, so the USA had to face that challenge and threat to Western democracy and free-market societies by all means possible.