The correct answer to this open question is the following.
The Vietnam War affected the United States in many aspects: in politics, in the economy, but in the social impact it had on the US citizens. It represented the longest war fought by the US Army and the one that was not won. The US government almost spent $168 billion in the ear effort, money much needed to be invested in the many problems the US had at that time. After the Tet Offensive, most American citizens began to seriously question the participation of the US in Vietnam. Tons of money had been spent in the war effort, many young lives had been lost. People started to mistrust the US government.