Hello again, everybody!  I'm not an expert on American presidential security procedures by any means, but I do have a few thoughts.  (By the way, Please. Please excuse my many typos - my right middle finger is broken, and it's in a metal splint, even as I attempt to type.  The only advantage of this is that I can make irreverent gestures, and people just assume it's my broken finger, but ever onward...)

First, back then in the 1960's, presidential security was obviously far more informal and free wheeling than it is today.  The implementation of vastly improved presidential security procedures was, no doubt, one of the unintended consequences of the Kennedy assasination.   JFK's security people should not have allowed him to do what he did.  That was one of their many flaws.

When George Bush senior was president, he visited the Boeing aircraft museum in Seattle, Washington, to give a speach.  We arrived at the museum several hours later after it was over, and heard the story.  The museum staff was still terrified!  The procedures (as far as the public was allowed to know them) went like this:  First, everybody arrived before the president.  And you had to be on the approved list.  Period!  And they really checked that list! They scanned it for months in advance.   A senior Boeing Vice President (of which there are many) decided he wanted to come.  Sorry - since he was not on the list. so they turned him away.    Finally, the President arrived.  How he got there, and when he got there were closely held secrets.  He gave his short speach and then left.  He left first.  How he left, and where he went were again secrets.  The people in attendance were held there for about two hours after he left before they were allowed to depart.  

Presidential and Federal Level VIP security had obviously improved.  These days those people are rarely seen in public except under tightly controlled situations.  They want to talk to the public - there's television.  I believe they're doing it right.