WASHINGTON, D.C. - President Barack Obama is promising to uphold the Constitution in a public swearing in ceremony that signals the beginning of his second term in office.

Placing his hand on two Bibles -- one used by President Abraham Lincoln at his first Inauguration and one used by the Reverend Dr. Martin Luther King, Jr. -- Obama took a public oath of office on Monday, after he was sworn in during a private ceremony on Sunday. The Constitution requires presidential terms to begin on January 20th.

Supreme Court Chief Justice John Roberts administered Obama's private swearing in on Sunday and the public ceremony Monday.

He also swore Obama in during his first inauguration in 2009.