He laid it out in an interview with Bloomberg Politics:
Cruz said his decision-making test on military action would be about whether there’s a “real threat” to American security. On foreign policy, he said he’ll employ a simple test: “How does it keep America safe? If it’s keeping America safe, we should do it. If it’s making America more vulnerable, we shouldn’t do it.”
Unfortunately, the Obama doctrine isn’t commutative. In the hands of a president with terrible judgment, it will still yield terrible outcomes. But good judgment alone doesn’t yield good foreign policy, and this is where the Obama doctrine becomes quite valuable. The foreign policy establishment in the U.S. is a font of terrible ideas and interests, constantly pressuring and tempting policy-makers to do stupid shit, and policy-makers with good judgment are not immune. In that environment, “don’t do stupid shit” is a good way to keep oneself moored.
The first question is whether Cruz’s conception of foreign policy is genuinely sound. I have many doubts. But assuming for the sake of argument that it is, Cruz is mainly just promising to ignore the constant profusion of nonsense emitting from our foreign policy eminences. That’s not so bad!