The secret service is not really on point protecting Trump most of the time.
If someone looked sideways at Obama they would already prepare to get in position and he did most speeches behind bullet proof glass.
With Trump, they just let him wander off across the North Korean DMZ or halfway down a runway to talk to the press.
Or people toss shit at the podium and no one reacts.
There's all the paparazzi making 'watch Trump golf' pictures too and the occasional arrest at the Mar-a-lago of a Chinese national with a USB stick
It might also have to do with technology (that they're using drones and such so they don't need as many 'eyes on the ground' anymore) but the contrast is clear.
With Boris, he actually got the question if he thinks he needs more security because he just rides around on his bike in London with people yelling wanker at him.
To which he answered that he doesn't believe that would make him safer and he didn't think it would be necessary.
You can say many things about Boris but he's not holding up in some ivory tower even though he gets the occasional egg thrown at him or a broken nose in the pub.
Reminds me a bit of our PM, who also walks or rides his bike across The Hague every morning to parliament.
In fact, if you take a stroll in the Hague near parliament there's a chance you'll walk into a secretary or minister walking to a different department.