January 20, 2009.
The swearing-in of a self-admitted foreign national as President of the United States.
The hard fact remains that if someone with standing brings a law suit to have Senator Cruz declared ineligible for the presidency it will go up to the SCOTUS and the precedent that there is does not look good for his being eligible. Although there is not firm decision on point in the SCOTUS there is a good bit of dicta and there is also evidence of Framers' intent that does not look good for his being found eligible.
The Great Pretender got a free pass and so did the late Edward Kennedy in Hopfmann v. Connolly, but I doubt if Senator Cruz would get such a pass, given the leanings of our judiciary.