Barack Hussein Obama became the 44th President of the United States even before he was administered the oath of office, thanks to a clause in the American constitution.
According to the 20th amendment of the US constitution, the term of President Obama begins at noon on January 20. However at 12 in the afternoon, Obama was yet to be sworn-in.
Obama took the presidential oath of office minutes after the clock struck 12 and so, according to the constitutional clause, he was already the President even before being sworn-in by Chief Justice John Roberts.
About two million people descended on the National Mall in Washington to witness the swearing-in of Barack Obama, the first African-American President of the US.