NSC-68 was outlined in your optional reading, but not in the excerpt from the IB text, so Secretary Acheson's defense may have been the first you have heard about it.
In short NSC-68 was a paper written by the UN Security Council that placed the policy of containment at the forefront of foreign policy. It stated that it was the responsibility of the government to not only 'contain' communism where it lay, but also it should take measures to thwart the potential for Soviet influence on other countries. NSC-68 justified US intervention in Korea and further solidified the US and the USSR as enemies.
The era after WWII redefined the notion of war and broadened the scope of executive power. How do you view Truman as not only the spokesperson against communism but also as the conductor--the person who actually commands ideology into action. How is this a change from earlier presidents?