Pure speculation.
Rush is talking about this right now. Trump wrote in one of his books he had published in the year 2000, 19 months BEFORE 9/11 that he thought a major terrorist attack in the U.S. would be “inevitable”. He wrote extensively in his book “The America We Deserve” about this. And that it was time to get down to the hard business of preparing for such an attack.
In other words, Trump, if he had been President then, would have taken steps in this country to prepare for potential terrorist attacks, and thus tighten up our security system. So, Trump is not talking out of his hat when he says things may have been different before 9/11 that may have helped to or even prevented a 9/11 if he had been President.
As illegal immigration is Trump’s big bugaboo, he most likely would have been looking at visa issues and tightening up requirements for foreigners getting visas. Trump was warning about loose security prior to 9/11 and George Bush at that time was doing nothing to tighten up security systems despite warnings from the intelligence community and other security experts about potential terrorist attacks. Once again Trump is right.