Presidents James Buchanan and Chester A. Arthur had Irish-born fathers (as did Andrew Jackson) and Mitt Romney’s father was born in Chihuahua, Mexico. Many Mormons had fled the United States for Mexico where they could practice polygamy without interference from the US government. I would hardly call becoming an expatriate, “allegiance.”
James Buchanan’s father emigrated to the U.S. from Ireland in 1783. When the U.S. Constitution was adopted in 1787 (and ratified in 1788), it conferred citizenship upon everyone living in the States. Therefore James Buchanan’s father was a citizen of the United States when James Buchanan was born in 1791. So, James Buchanan was a natural born citizen.
Chester Arthur routinely lied about his family background in a successful attempt to hide the fact that his father was not naturalized at the time of his birth.
More on that, here:
http://naturalborncitizen.wordpress.com/2008/12/06/urgent-historical-breakthrough-proof-chester-arthur-concealed-he-was-a-british-subject-at-birth/
Article II, Section 1, Clause 5, allowing anyone who was a “Citizen of the United States” at the time of the adoption of the Constitution to be eligible to be President rendered Andrew Jackson eligible.
...and Mitt Romney’s father was born in Chihuahua, Mexico.
The Mexican constitution of 1857, in effect at the time of George Romney’s birth in Mexico, provided only that those born of Mexican parents were Mexican citizens. So George Romney was never a Mexican citizen.