2010 Census Reapportionment: Pennsylvania lost one electoral vote, giving it 20 through the 2020 presidential election. Prior to this Census, the state had lost at least two electoral votes in every Census since 1960.

Pennsylvania, where the U.S. Constitution was written, was the second state admitted to the Union, officially becoming a state in December 1787. The Keystone State has participated in all 57 presidential elections through 2012. Pennsylvania is generally considered a battleground state, although it has voted Democratic in the last six elections. In 2012, Barack Obama won over Mitt Romney by about 5%. While still an important prize, with 20 electoral votes, Pennsylvania, like many industrial northern states, has seen population migrate away in recent decades. Peaking at 38 electoral votes in the 1910s and 1920s (second only to New York), the state has lost 45 percent of its electoral clout in 80 years.