20th Amendment
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 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.
When Obama first introduced Biden in public as his running mate, Obama called him the next president then he corrected himself by amending his statement by saying the next vice president.
If Barry Soetoro does not qualify after the Electoral College meets, then Joe Biden becomes Acting President — that much is clear from the 20th Amendment.
How, then, does a potential president qualify? By vote of the House of Representatives? The next election? At that point, Biden would revert to his proper role as Vice-President, but how do you get there?
The more I think about it, the angrier I get at Mr. Soetoro.