Unless it was deliberate by some higher-up. Find the least experienced and least competent agents and get as many of them as possible to Trump's team, so if something happens they will not get in the way.

Either a passive-aggressive way to endanger Trump just because somebody in the system doesn't like him, or is trying to suck up to some of his opponents. Or - well, if we assume that the security team had a mole or moles who were actually actively trying to get him killed and knew beforehand that there would be an assassin that day, it would presumably have been only one to very few individuals. In which case of course they would have wanted as few as possible of the other agents to be competent and experienced.

Unless it was deliberate by some higher-up. Find the least experienced and least competent agents and get as many of them as possible to Trump's team, so if something happens they will not get in the way.