The difference between Cruz and Trump is that Cruz is a thinker and Trump is a doer.
Cruz brings to the party a deep understanding of the text and meaning of the Constitution, and let's assume he knows the 800-year background of it, starting with the Magna Carta. And also the ancients – the Greek city-states and the Roman Republic. He knows the history of the Constitution in the U.S. as formed by Supreme Court decisions.
What Trump understands is the human action that has been enabled by the Constitution. He sees the human results – the consequences – of the Constitution: private property (Yes, I know, eminent domain; let's not get distracted. I mean the philosophical meaning of private property – transactions, ownership of labor, etc.), enforcement of contracts, individual liberty, public safety, etc.
So when Trump sees unlimited migration destroying the country, he sees that as a fact on the ground – the result of liberal (anti-constitutional) policy – but he sees it as a problem not because Hayek wouldn't like it or Friedman wouldn't like it or de Tocqueville wouldn't like it. That is not how Trump is coming to his conclusion.
He sees the results of a catastrophic policy. He isn't interested in the philosophical antecedents of that policy – the Frankfurt School, Herbert Marcuse, John Dewey, Marx, etc. That is why conservatives think Trump is an ignoramus, in the words of George Will. They don't understand a man of action when they see one.
The idea that Trump either doesn't know or plans to rip up the Constitution is absurd. Trump is not an uneducated man. And he is pro-American. That is the entire point of his candidacy – looking out for America's best interest. It is nice that Cruz spent his childhood memorizing the Constitution, but the Constitution is not that hard to understand. Trump knows that for some new policies he will have to get them passed by Congress, with all that implies. Why do you think he keeps talking about his negotiating skills?
There are some of his important policies that are under the purview of the executive alone. For instance, the wall. Congress already passed a law for that in 2006. It is just that neither the Republicans nor the Democrats built it (excluding a miserable piece of fence). For vetoing TPP, Trump doesn't need Congress. So it is a mosaic.
Coming into Washington with a mandate based on policies that he took to the public and then was elected on would give Trump enormous prestige and leverage. It is what the political scientists say an election should be about, and then once they get one, they all call for a glass of warm milk.
Lastly, talking about a "true conservative," the country doesn't exist to produce true conservatives; true conservatives exist to produce the country. Conservatism is a means to an end, not an end in itself.
So you tell me: what would Hayek say about our migration problem? Isn't this a situation with the individual maximizing his welfare, acting on his knowledge?
What would he say about temporarily stopping Muslim immigration? What is the "conservative" position on it? That is a bit cloudy, as every conservative in public life joined with liberals in condemning Trump as racist, foolish-because-it-was-impossible, as creating a police state when he introduced it. Cruz denounced Trump for advancing the idea. So "conservatives" – like Cruz – were for essentially unlimited Muslim immigration, as we know screening is a joke.
The only problem is that 70% of the public supported Trump's policy. Some candidates – like Cruz – have modified their opposition to a halt now that Trump has made it safe to do so and shown them the wisdom of doing so. Trump pointed out that Brussels was a bomb waiting to go off several weeks before it did.
So on a pretty critical issue, a "pure conservative," unguided by Trump, did not want to take steps to protect the country in a war-like situation. Trump saw that as a bad idea.