It happened on October 26 just after 11:15 a.m. in Whitpain Township.
Police say they were called to the Montgomery County Republican Committee when a staffer reported that a man had called the office and called him a slur.
The staffer then reportedly mocked the caller, which is when police say the suspect threatened to "shoot the place up" or "blow it up."
Whitpain Township police later tracked the call to 39-year-old Edward Cieri Jr. from Philadelphia, investigators say.
Cieri was arrested and charged with threatening to place weapons of mass destruction, two counts of terroristic threats, and harassment.
"This defendant crossed the line into criminal behavior when he threatened to physically harm a political staffer and threatened violence against a political office," District Attorney Kevin Steele wrote in a statement. "We are committed to a fair, safe, and free election, and all of Montgomery County law enforcement is committed to acting swiftly to investigate any threat of violence related to this election and arrest the individuals involved."