That was in a building, right?
I'm not sure I would consider a rally in a public place out in the open as a reason to disarm the public. I can certainly see them (the Secret Service) doing so, but I don't think it's right. The law says we have a right to carry in a public place. Of course, I'm sure there are special Secret Service rules that override that, somehow, not that I have any knowledge of those.
What if I'm going about my business, carrying concealed as usual, and happen to walk into a rally for a political candidate that I did not know was scheduled? Am I not allowed to pass through the crowd in the parking lot on my way into the mall or whatever other place I'm going because of my firearm which is being legally carried?
Stupid laws, stupid rules, stupid people effing things up for everyone. I have less and less patience for stupid, inconsiderate and needlessly violent people as the years go by. They are the ones to blame for politicians overreaching and attempting to restrict freedoms. Feckin' idiots.
If the candidate has USSS protection, they fall under federal law and yes, SS will restrict the ability to carry for anyone (LEO or not) who hasn't been cleared to do so. In some cases (Hillary private fundraisers), they've gone so far as to restrict access on public roadways that pass the event location (private homes), which I think is a clear exceedance of their authority.
Gotta keep those wealthy private donors from being revealed to the public!