In a comment to my post on President Obama's incorrectly recited oath of office, blogger Ted espouses the view that, because President Obama did not take the oath of office at noon Eastern Standard Time on January 20 (his incorrectly worded oath took place at 12:06 p.m. E.S.T.), it created a vacancy in the office of the president and Vice President Joe Biden succeeded to the presidency.
That is a cute argument, similar to the one used by some to promote the mistaken notion that David Rice Atchison was actually our 12th President (see http://en.wikipedia.org/wiki/David_Rice_Atchison#The_President_for_One_Day), but it ignores the fact that the presidential oath mandated by Article II, section 1, clause 8 of the Constitution is necessary for the "execution of [the] office" (i.e., for performing presidential acts, such as signing bills into law), not for accession to the office. The 20th Amendment to the Constitution makes clear that the new president’s term begins exactly at noon on January 20, and nowhere in the Constitution does it say that the presidential term does not commence until the president has taken his oath of office.
The view that not having taken the presidential oath creates a vacancy in the presidency also begs the question of how a person would be entitled to take the presidential oath (and afterwards begin to execute the office) if he had not become president beforehand. Had, say, Hillary Clinton taken the presidential oath on January 20, she would not have become president, because Article II does not provide that the oath makes one president, merely that if one has become president pursuant to the Constitution one needs to take the oath in order to carry out presidential acts. In the case of President Obama, he became president exactly at noon on January 20, 2009, as per the 20th Amendment, by virtue of having been elected president by the Electoral College.
So, no, Joe Biden was not our 44th President, not even for the six minutes before President Obama's attempt at taking the oath of office.