PHILADELPHIA — Pennsylvania’s high-stakes U.S. Senate race is expected to get a new contender in the coming weeks, when Montgomery County Commissioner Val Arkoosh joins a contest that both parties see as vital to control of the chamber. Arkoosh would become the third elected Democrat in an election drawing intense interest from both parties — even though it’s more than 18 months away. She will enter a growing Democratic field that already includes Lt. Gov. John Fetterman, of Allegheny County, and state Rep. Malcolm Kenyatta, of Philadelphia. Arkoosh has long been eyeing the Senate race, but is…
