The most hardcore and informed JFK conspiracy researchers are convinced that Secret Service protocol was deliberately altered by the conspirators.  Another component is redundant venues for the hit.  They may have been close before Dallas and if they had failed in Dallas, there would have been another set of arrangements.  This is a point lost on many people.  That everything didn't *have to line up* in Dallas.  If not Dallas today, then somewhere else tommorow.  With a different patsy?