Chester Arthur was born in 1829. There was no dual citizenship at that time in America. His father had not yet become a citizen. So Arthur was a British subject.
Yes, if Birtherism is correct, Arthur was not a "natural born citizen." But he was elected to the Vice-Presidentcy, and served for years as President. So, either:
A. Arthur was ineligible to be elected to either the Vice-Presidentcy, or serve as President, and everybody back in the 19th century was just too stupid to understand that; or,
B. Birtherism is wrong.
Which is more likely?