Trump, I believe, does have a point, W Bush did not keep us safe. But context also matters. If we are playing the ridiculous game that everything is the fault of the POTUS, which many like to do, then this criticism of Bush of fair. I don't think the information released after the fact about what was going on in the days prior to 9/11 do Bush any favors in making his people look competent. I believe Bush placed enormous trust in Cheney in his little cabal of neocons who ultimately were very incompetent in pretty much everything they did. Whether Bush could have made better choices all by himself remains an open question to me. But to Jeb's point, Trump does strut around spewing that this is all so simple and all you have to do is be a tough guy and negotiate hard deals. The people supporting Trump are loving this shit because it is so Reaganesque, and nails that dismissive "There you go again" tone while delivering nothing of substance. Jeb's walking a fine line here though, he's trying to criticize the Republican primary as being like a reality show without actually naming who he's really annoyed at, which are the people who are supporting Trump whose votes Jeb wants.
Seems like the Donald is a bit off in his timing. The 19 hijackers apply and receive a total of 23 visas at five different posts from November 1997 through June 2001. Hani Hanjour, Khalid Almihdhar, Saeed Alghamdi and Ahmed Alnami, Saudi citizens, apply twice at Jeddah. Only Hanjour applies for a student visa, others for tourist/business visa.