i read the advance team is often in the clear. If they encrypted, thats ok, my scanner mutes encryption. years ago the advance team used usss baker channel, i assume that changed.
Over the decades, there's been a lot of utter BS posted about these sorts of comms. The best thing you can do is gather-up whatever freqs you can find from online lists (some of them now are long-obsolete) & scan them plus search the VHF/UHF federal spectrum during a visit, from as close as you can reasonably be.
WHCA Advance Team operations aren't as lengthy as they used to be, thanks to advanced technology that's small enough to where they can have several redundant long-haul systems.
In the old days, it was getting to the area about a week (longer, for overseas visits) in advance & setting up some remote VHF/UHF bases & testing them, coordinating with AT&T & the local telco for redundant, priority phone trunk circuits, etc. & having some sort of HF capability -- a portable station set up, or using Roadrunner's (WHCA mobile comms vehicles, established in the late 1970s) HF capability, or sometimes maintaining a VHF/UHF radio link to the presidential aircraft, which could then relay long-haul comms onward.
Thanks to both satellite comms as well as good cellphone technology, a lot of the old infrastructure that would take many days to plan, set-up, troubleshoot, etc. (& during the process, alert people with the right freqs in their scanners that a yet-unannounced POTUS visit was coming up soon) has been replaced with reliable, redundant, highly portable gear that doesn't rely on a lot of local infrastructure, thus not the same sort of WHCA ADVON comms that we knew & loved up until about 15 years ago, *and* the technology continues to improve...
That said, yes, with the right freqs or search criteria & being within range, you should absolutely hear WHCA, SS, & SS PPD comms when POTUS is in town (also VPOTUS to a lesser extent), and while most should be encrypted, as recently as September 2014, I heard non-secure, operational comms on a well-known VHF freq associated with WHCA/SS & in-use for a VPOTUS protective detail.