Pennsylvania’s U.S. Senate race is one of the most watched races in the country.
The open seat, being vacated by Sen. Pat Toomey (R-Pa.), is pivotal to the Senate’s balance of power. It hasn’t been held by an elected Democrat since 1969, although longtime Republican Sen. Arlen Specter switched to the Democratic Party in 2009 while in office. Specter served from 1981 until 2011, when Toomey was elected.