How many presidents have chosen to affirm (rather than swear) to "faithfully execute the office ... "? Try your hand at inaugural trivia.

"Being true to our founding documents does not require us to agree on every contour of life; it does not mean we will all define liberty in exactly the same way, or follow the same precise path to happiness," he says. "But it does require us to act in our time."

Unlike with his first swearing-in, Barack Obama does not face two ongoing wars and an economy on the verge of collapse. But thorny issues remain, and there's less hope than there was four years ago that Obama can bend Washington to his will.

Obama fulfilled the constitutional requirement to take the oath before noon on Jan. 20. He will repeat the oath in public on Monday.