See here. Even if his comments cited by Ponnuru aren't representative of what Trump would do in office, why trust him? Why take the risk when such better presidential candidates are available?
Trump supporters often cite illegal immigration as a major, primary, or sole reason to vote for Trump. But think of all the steps needed to get to the point where Trump's position on illegal immigration would be implemented. You have to:
1.) Think he'll get elected, despite his big electability problems.
2.) Think Trump will do what he says he'll do, despite his character problems and long record of inconsistencies.
3.) Think the Republican Congress, who Trump supporters keep denouncing, will pass his immigration plan.
4.) Think the judiciary, including judges appointed by Trump in the future, will refrain from significantly altering his immigration plan once it's enacted.
Let's see if people like Rush Limbaugh and Sean Hannity give prominent attention to the issue Ponnuru has raised, putting it at the top of their radio programs and denouncing Trump in strong terms, as they would if Ponnuru's post were about somebody like Jeb Bush or John Kasich instead. And let's see if Evangelicals and other people supporting Trump do enough research, and have enough discernment, to find information like what Ponnuru writes about and react appropriately to it. Or will they just keep following the lead of Limbaugh, Hannity, et al. so uncritically?