Here are five things to know about the controversy surrounding Cruz's Canadian birthplace:
1. The U.S. Constitution states that "no person except a natural-born citizen, or a citizen of the United States, at the time of the adoption of this constitution, shall be eligible to the office of president." Constitutional scholars have long interpreted that sentence to mean that at least one presidential parent must be a U.S. citizen — not that a White House occupant must have been physically born on American soil.
2. Two lawyers who represented both Republican and Democratic administrations recently argued that Cruz meets the requirements. "Cruz has been a citizen from birth and is thus a 'natural-born citizen' within the meaning of the constitution," Neal Katyal and Paul Clement wrote recently in the Harvard Law Review.
3. It's a trouble spot that has reared its head before. Mitt Romney's father, George, ran for president in 1968. Although his parents were American citizens, they resided in Mexico when George was born. Romney left the race before his birthplace became a serious issue, but constitutional experts agreed that his American citizenship met the requirements.
4. As recently as 2008, U.S. senators passed a resolution that allowed John McCain to run for president even though he was born on a military base in the Panama Canal Zone. It was an unnecessary move, however, given a law passed in 1937 that, applied retroactively, gave citizenship to anyone born in Panama whose mother or father was a U.S. citizen.
5. Congress has attempted to clarify the issue. Former Republican senator Don Nickles introduced the Natural Born Citizen Act in 2004 to make clear the term includes the children of U.S. citizens, or those under 18 who were adopted by American parents. It never passed the Senate.
Follow Lee-Anne Goodman on Twitter @leeanne25