Section 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.
So, in the case at hand, assuming 0 cannot produce proof and the EC demands it, the President will not have been chosen by Jan 20, so Biden would be the acting President until they can get a President who qualifies.
I have never heard of any legislation or U. S. Code that covers the situation and authorizes the Congress or anybody else to qualify a President, so if all that actually transpires (unlikely) we would have an Acting President Biden for 4 years. Wow!
I say it's unlikely because if the EC demands proof and 0 doesn't provide proof, then I think the Dim electors in the EC would vote to select Biden as President. Maybe it would devolve to the Senate (the new Senate) to choose a VP at that point.
Perhaps if one or more of McCain's electors is made a party to a re-filing of Berg's lawsuit, the Supreme's may consider him to have standing. If an Elector does not have standing to challenge the qualifications of a candidate, then NOBODY does, and that section of the Constitution has no meaning.
So far I don’t think the SCOTUS has requested nor has indicated Obama needs to show proof. I think the respond thing is for his attorneys to respond with anthing they wish such as motions, etc.
After Obama is elected via the EC then that is one thing but prior if Obama should drop out I’m not sure. I know that the DNC has authority to replace him as the Democratic Party nonimee up to some point. That point is which I don’t know where is located along the process time table.