Three countries have a claim on Cruz. Canada by operation of natural and positive law, The US by operation of positive law (8 USC), and Cuba by operation of positive law.
If Cuba's positive law reads like US positive law, what makes Cuba's claim inferior to the US, at Ted's birth? What is Ted, the NBC of three countries?
That's absurd.
Based on the precedents of Barry Goldwater, George Romney, John McCain, and Barack Obama, yes he is. To hold Cruz to a different standard would be an arbitrary and capricious application of the law.
SCOTUS will defer to the Electoral College on the issue. Obama's election and re-election is proof of that.
What is Ted, the NBC of three countries?
That's theoretically possible. For example, under Panama's constitution, John McCain was an NBC there too when born on a U.S. military base in Panama. He was also a U.S. NBC.
When a dual citizen minor becomes an adult, he is supposed to choose one citizenship over the other (assuming he knows about it). In practice, that rarely happens.
For example many dual NBCs (particularly U.S.-Canadian) keep both. It's only been with the implementation of the U.S. Foreign Account Tax Compliance Act (FATCA) reporting requirements that you're seeing a trend by dual NBCs living in Canada to renounce their U.S. citizenship as adults.