I have an opinion piece at Reuters, Natural-born mess: What would it take to kick Ted Cruz off the ballot? It begins:

Donald Trump has resuscitated questions regarding Texas Senator Ted Cruz’s eligibility to serve as president of the United States. Cruz was born in Canada to a Cuban father and an American mother. A recent Trump tweet succinctly pressed the issue: “Sadly, there is no way that Ted Cruz can continue running in the Republican primary unless he can erase doubt on eligibility. Dems will sue.”

The U.S. Constitution requires that the president be a “natural-born citizen” of the United States. Though many contend that being born to an American mother is sufficient, others say only those born on U.S. soil are eligible.

What would a legal challenge to Cruz’s eligibility look like? It’s far more complicated than you might think because it depends on how each state handles his access to the ballot. New Hampshire’s Ballot Law Commission, for example, has already said that Cruz is eligible — at least until a court says otherwise.