Should a question be marked as a duplicate if there's already an applicable answer on a different question?

Question

Recently my question Could the Senate confirm a new Supreme Court Justice without holding any hearings? was marked as a duplicate of Why are SCOTUS appointee Senate hearings not mandatory?. The two questions arguably different - mine is about nominating a new justice without a hearing, the other is about refusing a hearing to a justice in order to deny them the nomination. However the answer to the older question contains the following sentence:

Theoretically, the Senate can confirm a nominee without holding any confirmation hearing as the requirement of a hearing is not mentioned in the Appointments Clause.

This does answer my question, however the two questions are not about the same thing. When I pointed this out, a comment pointed out the following:

When a question is closed as 'Duplicate, it says, This question already has an answer here. Thus duplicates are based on answers, not questions. See, Why are some questions marked as duplicate?. "The fundamental goal of closing duplicate questions is to help people find the right answer by getting all of those answers in one place." While the questions are different, it happens that the earlier question answers both that question and this question.

Is this the official policy on Politics.SE? On Travel.SE the policy is that the questions must be the same to be marked as a duplicate: A friendly reminder that duplicates should be the same QUESTION, not different questions with similar answers.

Answer 1

I cannot address the "official policy on Politics SE" (I don't know that there is one); but there is a policy (of sorts) for StackExchange.

What I will suggest is that, in the absence of an official policy for Politics SE, the policy for StackExchange applies.

From an answer on meta.stackexchange, How should duplicate questions be handled?

When are two questions considered duplicates?

According to Stack Exchange co-founder Joel Spolsky, we should only close real duplicates, and according to co-founder Jeff Atwood, there are three kinds of duplicates: cut-and-pastes, accidental duplicates, and borderline duplicates (requiring judgement as applied by the community).

Questions may be duplicates if they have the same (potential) answers. This includes not only word-for-word duplicates, but also the same idea expressed in different words.

Questions asking about the same aspect of the same concept, but with different examples, may or may not be considered duplicates. It depends how easy it is to figure out one example from the other. If it's only a matter of changing one small part of the question (e.g. in the case of coding sites, some numerical values or some variable names), they're duplicates. If understanding why the questions are at all related requires a detailed explanation, the questions aren't duplicates, merely related.

Expanding from Jeff Atwood's blog, Handling Duplicate Questions,

Borderline duplicates. These questions are ambiguous; they’re in the same ballpark as a previous question, but have subtle differences that may make them legitimately standalone questions. These are subject to interpretation. We rely on Stack Overflow users to tag these questions appropriately so they naturally “group” with the questions they’re related to. The more tags the questions have in common, the more likely they are to show up together on the related questions sidebar. You can also edit in links to the possibly duplicated posts, if appropriate, but be sure to make the tags match so the system can figure out the relationship without as much manual effort. There’s often benefit to having multiple subtle variants of a question around, as people tend to ask and search using completely different words, and the better our coverage, the better odds our fellow programmers can find the answer they’re looking for.

Borderline duplicates "requir[e] judgement as applied by the community"; but are not duplicates "[i]f understanding why the questions are at all related requires a detailed explanation". However, "[t]here’s often benefit to having multiple subtle variants of a question around".

How meta.stackexchange handled We as a community overuse the duplicate feature is instructive.

Answer 2

Yeah, I agree that such borderline cases are debatable whether they should merely be closed. I don't know if this is good practice or not, but in one such case where the answer was included in a larger answer to another question, I copied out the relevant portion of that answer and posted it as community wiki (under the new question). Although I didn't vote to close that question, it was apparent to me that it was going to get closed as there were 3 or 4 pending close votes (with the duplicate reasons) when I have done that quote-copy.