I've enjoyed the debate over whether Ted Cruz, now running for the Presidency, is eligible to serve. The Constitution requires that the president be a "natural-born citizen" of the United States, a phrase that the Supreme Court has touched on three times, most recently in 1875. In those three early cases (The Venus, 1814; Shanks v. Dupont, 1830; Minor v. Happersett, 1875), the Court suggested that citizenship extended to persons born in the United States to parents of whom at least the father was a United States citizen, without, however, explicitly defining the constitutional term.
Senator Cruz was born in Canada to an American mother and a Cuban father. Under the law of the United States, he became an American citizen at birth. So he is a "natural-born citizen." Yes?
Not so fast, maybe. It's possible that not all persons who are citizens at birth are natural-born citizens. The wrinkle is the Fourteenth Amendment, ratified in 1868, which includes as its first sentence: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside." A court might find, if it undertakes to decide the question, that the Fourteenth Amendment defined natural-born citizens to be only those persons born in the United States and subject to its jurisdiction (so excluding children of foreign diplomats). Congress, the court might say, has the power to extend citizenship at birth to other classes of persons, including children born abroad to American citizens, but has not the power to change what has been from 1868 the only constitutional definition of "natural-born."
I imagine that if someone sues a secretary of state to keep Senator Cruz's name off the ballot on the ground that he is not a natural-born citizen and therefore not eligible to serve, any lower court faced with the case will hold that it is a political question and not one for the courts. If the question is political, then elected officials would have to rule; for example, had Senator Cruz run four years ago and faced a challenge to be listed on the Oregon ballot, the question would have gone first to Oregon's secretary of state, our now-Governor Kate Brown, who was born in Spain.