Two presidents were Quakers (Herbert Hoover and Richard Nixon) and information about their religion is harder to come by. Quakerism is, by its nature, not circumscribed by doctrines, but even so it is hard to determine whether either Hoover or Nixon had much adherence even to Quaker practice. For instance, it is common among Quakers to refuse to swear oaths; however, recordings show that Nixon did swear the oath of office in the conventional manner in all cases, and while the matter is clouded for Hoover, there is newspaper and circumstantial evidence that he did likewise. While Abraham Lincoln never officially joined a church, there has been some research indicating that he may have had Quaker leanings. During his time in office, he had numerous meetings with Quakers and had investigated a supposed Quaker ancestry.