Citizenship is naturally inherited from one's parents. A child born to German Citizens is a Natural Born Citizen of Germany and a child born to Spanish Citizens are Natural Born Citizens of Spain.
Citizens of the United States that do not qualify as Natural Born Citizens are classified as Native Born or Naturalized Citizens Only Natural Born Citizens are eligible to serve as the President or Vice President of the United States.
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It is interesting that the 3rd in line for the Presidency, in worse case scenario, the Speaker of the House, is not subject to the same exact Natural Born Citizenship requirements.