I'm going to get a little nitpicky here myself, but most of the photos Flabi posted showing that leaving the president is the norm just doesn't pass my smell test.
This one appears to be taken on an Airport runway, there are unmanned motorcycles in the foreground and the Agents in the background aren't even in their car yet. Clearly this motorcade is not even running yet.
This one appears to have been taken in Honolulu during JFK's visit in June of 1963. While there are no agents apparant in this close-up image,
this short video clearly shows agents running alongside his rear bumper.
This next one is taken in front of the Washington Monument in DC, the "home-base" of the president, and what I would consider a secure and fortified location.
Washington
Washington
And while I can't tell where the other 2 photos you provided were taken, I don't think you can either.
While I've provided the source and relevant date of my images, you have yet to show where you sourced these images from, or when they were taken. For all we know they could all have been taken in during JFK's inaugural parade in 1960 when there wasn't a looming threat on the presidents life.