One would think that this was would be conveyed by the context. EVERYONE has a responsibility to enforce this law. The primary line of defense SHOULD have been the State Election officials who should NOT have let him on the ballot until they had seen proof of some sort. (Beyond an affidavit from that insane IDIOT Nancy Pelosi.)
"The underlying problem is that the Constitution says that you have to meet thus-and-such requirements to be President, but doesn't say who is supposed to determine whether or not a particular person does, in fact, meet those requirements."
Actually, the Twentieth Amendment, Section 3 has the answer to BOTH of these statements.
"3. If, at the time fixed for the beginning of the term of the President, the President elect shall have died, the Vice President elect shall become President. If a President shall not have been chosen before the time fixed for the beginning of his term, or if the President elect shall have failed to qualify, then the Vice President elect shall act as President until a President shall have qualified; and the Congress may by law provide for the case wherein neither a President elect nor a Vice President elect shall have qualified, declaring who shall then act as President, or the manner in which one who is to act shall be selected, and such person shall act accordingly until a President or Vice President shall have qualified."
A few notes.
1. There is no such position as a "President elect", legally, until such a time as Congress has accepted the results of the electoral college votes and a person is actually named as the "President elect". This means that the term "shall have qualified" refers to something other than the results of winning an election. There is only one place left in the Constitution having to do with "qualifications" for the office of President, that being the eligibility requirements from Article two.
"No person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty-five Years, and been fourteen Years a Resident within the United States."
2. Since it is the duty of Congress to name an interim President in the event of a President elect's "failure to qualify", they, Congress, must know whether or not to do so. This means that they, Congress, must be aware of whether or not a President elect meets the eligibility requirements from Article two. It is the burden of the President elect to "qualify" or "fail to qualify", thus NOT proving one is eligible under Article Two to Congress is the same thing as "failing to qualify." Congress avoiding its duty to uphold Section 3 results in the same "failure to qualify", something they may have done on purpose in this instance depending upon the reasons why. National security? Who knows at this point.
3. How was Obama's eligibility proven to Congress without a valid long form birth certificate? He apparently does not possess such a thing or we would have seen it a million times by now.
4. The eligibility requirements start out with two simple words which forever preclude anyone who "fails to qualify" from serving as a legal president, "No person". Someone who sneaks in because Congress failed to uphold it's responsibility to enforce the Twentieth Amendment, Section 3 doesn't legally exist. The Constitution cannot be fooled just because Congress didn't act when it was supposed to. A President elect either qualifies or he cannot ever be President, period.
Thus it is that we have protection from someone who is ineligible to serve as President already written into the Constitution. Unfortunately, we also have a Congress that did not uphold it's oath to support the Constitution and a usurpation of the office of President is the result. We know he is illegal strictly on the basis that we don't know if he is eligible. If he "qualified", there would be no debating the subject. The fact that nobody in Congress is able to say whether or not he is eligible means that he never proved to them that he was and thus has "failed to qualify".
Now, as to who has "standing". Any elected official at the state or federal level who took the oath of office in Article Six has standing, to demand that the Constitution be obeyed. This means that no judge can deny them the enforcement of their oath to "support the Constitution" if they have a question about whether or not any portion of that Constitution has not been adhered to. In this case, the Twentieth Amendment, Section 3 has clearly been IGNORED by the primary party instructed to act under it, Congress.