I also believe that travel by POTUS and VPOTUS are at times fronts for getting USSS and other players into the target area under the guise of "advance security" operations/preparations.
I've been frustrated at the USSS failure to prevent this mess by reporting Clinton's and Obama's more obvious treason/treachery, since they were there.
Good question.
I do know that even though POTUS praises USSS, he trusts and relies on USMC and private bodyguards because USSS has some haters still there.