Bold above by me -
Maybe others have already shared this info, but local reporters (CBS affiliate in Pittsburgh) interviewed the Butler Township Manager, Tom Knights, in a July 17 broadcast (link below). Mr. Knights said that Butler Township Police informed SS 2 days prior to the rally that they (Butler Township) didn't have the man-power to do anything but cover traffic at and around the event. The interview segment also states that SS did not confirm nor reply to that message. The reporter is initially unclear who the officers inside the building were: at first mention in the interview, she just calls them "police," which doesn't narrow it down for us here, but later calls them "local SWAT team members," and the Township Manager confirms that.
I will point out that there are both a Butler *Township* Police Department (the Farm Show facility is in that township) and a Butler *City* Police Department (Butler is the city where the hospital is that the former President was taken to). In other parts of PA, it's possible for a "township" and a "borough" (or city) to have the same name but totally separate governance and services (even though geographically, the borough may be completely surrounded by the township). But a search for Butler PA SWAT doesn't turn up any clear info (except a page for the Sheriff in Butler County, OHIO) about who the SWAT team works for.
Maybe someone else understands more clearly.
Interview link:
(This appears on the station's verified YouTube channel on July 17 - admins, please delete if YouTube's off-limits here)