President of the United States: I have received over 2,000 letters on

The correct answer to this question should be D. This is a weaken the argument question, and the first step to solving it would be to ID the conclusion. In this case, it is that "most of the people in the country agree with" the president. Hence, we have to look for information that suggests people don't agree, or undermine the evidence given in favour of the president.

A - So what? If many people have strong opinions on the issue, it still doesn't tell us whether that opinion is in favour of or against the president, which is the crux of the question. OUT

B - This information is not helpful in any way. So what if some members disagree? It doesn't tell us whether that 'some' is more than half. Moreover, this is members of Congress, whereas the conclusion is regarding the people as a whole. OUT

C - This info tells us nothing about the conclusion either. We do not care about the strength of the (dis)agreement, only the numbers. OUT

D - If this is true, it undermines the evidence the President has given. His argument is based on the fact that lots of people wrote to him agreeing with the decision. But if those who write are the same as those who agree, it becomes less likely that the president has overall popular support. This answer is therefore CORRECT.

E - So what if the position changed? We only care if the people agree with the president's current position. This point gives us no further information on that, so it's irrelevant. OUT

Remember that in order to weaken an argument, an option may:
1) Introduce new information that hurts the conclusion
2) Undermine existing information in some way (like in this question)

- Matoo