Yes! I have been on three different Presidential security details as a military back up to the secret service. What I know for fact is that only the current sitting president gets the "real" secret service, and the non-seated -presidential candidate gets the customs, IRs, border patrol and other pools the secret service can pull from in times of campaigns. Their training and skill sets are terrible and most of them hate being pulled and mandated to be the backup secret service members.
That is why the president flies on Airforce One (US Airforce pilots and crew with fighter plane escorts) Marine One Helicopter (Marien pilots and crew). And we were added to test or back up for the seated US president that you the citizen never knew we were there as US Army.