I saw this post purportedly from "Kate" and decided to check and it is quite correct.
Pennsylvania State Nicknames
Whereas there is only one Pennsylvania motto, there exist a number of state nicknames for Pennsylvania:
"The Keystone State"
This term is originally found in the language of architecture. It designates the middle stone of a stone arch - the central, important stone that keeps all the stones in place.
In relation to Pennsylvania the meaning is symbolic: Pennsylvania is placed in the middle of 13 colonies thereby playing a central political, social and economical role.
https://www.inspirational-quotes-short-funny-stuff.com/pennsylvania-state-motto.html
As a Britfag with zero previous interest in local politics due to the overt and covert corruption and even less in US politics, I have a question for USfags.
In terms of the mid-terms, how important is Pennsylvania? Could it actually be key?