United States : The Constitution provides that "No person except a natural-born citizen, or a citizen of the United States at the time of the adoption of this Constitution, shall be eligible to the office of the President; neither shall any person be eligible to that office who shall not have attained to the age of 35 years, and been years a Resident within the United States." Although US law protects dual and even triple citizenship, no US president has ever had either. In the late ’70s, secretary of state Henry A. Kissinger, a naturalised US citizen born in Germany, was barred by the presidential qualifications clause from his office’s legal place in the line of succession to the presidency.