As in 2009, this time, too, President Barack Obama will be sworn in twice. In 2009, Chief Justice John Roberts Jr fumbled while administering the oath of office during the inauguration ceremony, so Obama had to take the oath again. January 20 – the day the president has to be sworn in, according to the US Constitution – was a Sunday this year, so there could be no public ceremony. Obama took the oath of office in a private ceremony at the White House. Justice Roberts made no mistake this time. The ceremony went off without a hitch. The public ceremony follows today when up to 800,000 people are expected to gather on the National Mall for the inaugural festivities. Presidents Dwight Eisenhower in 1957 and Ronald Reagan in 1985 also had to be sworn in twice when their second terms commenced, a private oath-taking ceremony on a Sunday followed by a public inaugural the next day.