Mr. Lubet is himself a dual citizen of Canada and the U.S., so he knows the intricacies of what i
s entailed in the process. (One which he notes he has no intentional of following, since he's quite happy with how things are.) However, it allows him a certain whimsy in bending over backwards to ponder why Ted Cruz hasn't acted on his word yet.
"Perhaps Cruz simply hasn’t gotten around to it," he writes. "In fairness, the Canadian government requires more than a simple shout-out before canceling somebody’s citizenship. The aspiring ex-Canadian has to pay a fee of $100 and submit an official 'Application to Renounce Canadian Citizenship,' which could be a bother for someone with a busy schedule of Tea Party meetings and lectures for the Heritage Foundation. On the other hand, the renunciation form is pretty simple. There are only 12 questions on the application, and most of them request basic information such as name, address and date of birth, all of which could be handled by a staffer."
However, eventually he gets to the problem for Mr. Cruz. And it's one particular question about providing proof, rather than just taking someone's word. And that proof might be hard to come by, even if the story is all true. But if you can't prove it and you get turned down, that could be a significant embarrassment and problem.
He explains here very well.