Johnson does want to make sure the Communists are dealt with and not ignored, as he says, 'if you start running from the Communists, they may chase you into your own kitchen'. This means that if the Communists are ignored, they will take over, spread and become a threat to US lands. He is referring indirectly to the US policy of containment where Communism has to be prevented from spreading and the Domino theory, which demonstrates how Communism could spread extremely quickly. Historians can make good use of these views of the President because his views are very important, as he was one of the main leaders in the Vietnam War. The source can also be useful to suggest that Source A is inaccurate because President Johnson has given a totally different account of why America should get involved with Vietnam. In Source A he is saying that it would be to preserve peace and allow the people of South Vietnam to have freedom, although in Source B he is arguing that it is not worth it, as the country is so far away and no use to America, which implies that one of them is inaccurate.
The source's usefulness is affected by the information that is left out, as it means that historians cannot use the source to find out the President's views on other issues. President Johnson doesn't mention why he wants to 'contain' Communism and why he does not like this system, which is partly because it means that the country cannot be as productive. In addition, he does not mention the Truman Doctrine or what his opinions are on it when he explains the only reasons they should go into war. This makes it less useful because historians will not be able to see whether Johnson thought it was worth sending supplies into Vietnam, because from what he says, he does not appear to think that Vietnam is a worthwhile country to get involved with. Johnson does not explain how he would feel about going into war against Vietnam if the Vietnamese caused a threat to America, other than the spread of Communism, like they did in the Gulf of Tonkin. Therefore, historians cannot justify whether he is saying Vietnam is not worth fighting for because they have been no real threat to America yet and whether he would actually change his mind if they became a threat. Johnson does not comment on why the public and politicians agree to get involved in Vietnam, which makes this statement less reliable because there is no evidence to back up this point. If what he is saying is correct, historians will be unable to find out why these people supported the war from this source, or what Johnson thought their reasons were for supporting war.
Some of the points that Johnson makes are accurate and correct, however some of the things he says are incorrect. When Johnson says, 'if you start running from the Communists, they may chase you into your own kitchen,' he is being accurate by saying this is a possibility because Vietnam attacked two American ships in the Gulf of Tonkin so they are prepared to fight the Americans. Also, they used the guerrilla tactics, which the Americans were not very good at fighting against, so they had the capabilities of causing threats to the Americans involving land. When he mentions the politicians by saying, 'they'd bring a President down if he ran out, wouldn't they?' he is being quite accurate because they may not like him being President if he is making America look weak by backing out of Vietnam and ignoring the situation. Because Johnson makes some accurate points, it makes the source useful for showing some reasons why Johnson felt he had to get involved in Vietnam. Some points that Johnson makes are inaccurate, for example, 'I don't think we can fight them ten thousand miles away from home' is inaccurate because they did manage to send thousands of troops and 3500 US marines, and used chemical weapons and search and destroy to fight against the Vietnamese government. Although he was unaware of this at the time, it still makes the source not useful for giving us factual details; its main uses lie in giving historians Johnson's opinions about going into war.
Source C is an American critic of the war, called Professor Noam Chomsky, being interviewed in October 1982. Firstly, this source's content can be trusted for providing historians with the possible reasons why America got involved with Vietnam, because he is a Professor so he is an intelligent man and probably has good abilities in research and gathering information. However, historians don't know what he is a professor of, and he could be a Professor of Science for example. Therefore he may not have studied the war in great depth, which makes the source slightly less trustworthy, and many US intellectuals were opposed to the war anyway so this source will not be as useful, as he will be making the same points as a lot of other US intellectuals. The source is trustworthy because Chomsky would have had access to more sources due to the interview being after the war. He will have been able to look at sources like a private conversation President Johnson was having, as well as photos of the destruction that was caused to South Vietnam. However Chomsky is anti-war and is known to be an extreme radical.
Chomsky refers to these sources as being 'official' and includes quotes around the word, which might suggest they are not. Nevertheless there is same justification in believing that the USA were not just defending the South Vietnamese against communism but protecting its own interests in the Far East. Chomsky states 'The U.S. did not want an independent South Vietnam.' This is justified by the fact that South Vietnam did not have free elections.