I think the military top brass such as General Kelly have him covered very well. We do know he brought in his own longtime known security team to be even closer to him than the USSS until he and the Generals had a chance to select those in the USSS that were 100% trustable.
Early on (Feb 2017) the Director of the USSS was fired (Joseph Clancy) although the media was writing that he ‘stepped down’. The backstory is he was fired because of security lapses notably one in which an intruder had penetrated the WH grounds walking around at night for 30 minutes testing to see if any windows were open that he could crawl through. There was a related story that the intruder was there to kidnap one of the President’s grandchildren.
Donald Trump did take security risks to his person. Early on in the campaign of 2015-2016, Donald Trump wore bullet-proof vests to his rallies. There was one rally where it was thought that shots had been fired at him and he scrambled to the back of the stage protected by his own security team. But his son Eric pleaded emotionally that the size of the crowds at those campaign rallies required USSS to engage because the President’s own security team was too small in number. People back then that traveled with and knew Candidate Trump said he was truly heroic for facing those huge crowds.
But now I think he must have the best security ever arranged for any President.
Blackwater is involved in his security as well if I’m not mistaken.