birther

Short definition from Wiktionary

Noun

1. 1
   One who gives birth.
2. 2
   A believer in the conspiracy theory that Barack Obama, 44th president of the United States (2009–2017), is not a natural-born US citizen, and was therefore ineligible for the presidency under the United States Constitution (Article II, Section 1).
3. 3
   More generally, anyone who questions the eligibility of a candidate for office based on their citizenship status.

Verb

1. 1
   To question the eligibility of a candidate for office or the location of one's birth.