Alternative theory:
Chester A. Arthur did not hide anything. He was born in the United States and was regarded as a natural born American. The fact that his father did not obtain American citizenship until after his son was born was known and not hidden, and not considered an impediment to his serving as Vice President, and after Garfield’s assassination, to his serving as President.
There were allegations made during his lifetime that he was born in Canada. He never replied to them, and certainly his enemies were looking through his past for anything to use against him. I presume they found out about his father’s citizenship status and regarded it as not affecting his ability to serve as Vice President or President.