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Although the error did not invalidate the presidential oath he took in front of 1.8million spectators in Washington, aides said White House lawyers advised the president to run through it a second time just in case.
Chief Justice Roberts and Obama went thought the drill again at the White House Map Room in front of a small group of reporters.
'We decided that because it was so much fun ...,' the new president joked before turning to face Roberts.
'Are you ready to take the oath?' he said.
'Yes, I am,' Obama replied. 'And we're going to do it very slowly.'