Obama took the oath of office a second time because Judge Roberts didn't read the oath exactly as the Constitution specified, and this caused Obama to likewise err. Gotta do it over. We wouldn't want to violate the Constitution.
Meanwhile, we're involved in two wars that were never declared by Congress, and the Constitution specifies that the Congress is to declare war. Using gold or silver as currency is illegal, though the Consitution says that only gold and silver are to be used as legal tender. The Constitution does not grant the federal government the authority to heap upon foreign nations money used to control their citizens, but we heap billions upon such nations. The Bill of Rights guarantees freedom of speech, yet certain political speech, such as say a paid television advertisement, is illegal for ordinary citizens in the weeks prior to an actual election. The fourth ammendment protects us from searches without probable cause. Apparently this means a state can't regulate abortion, but doesn't mean that the government can't monitor our internet usage or phone calls.
So why bother with a second oath. The Constitution is already irrelevant.