From NBC's Chuck Todd and Domenico Montanaro
Exit pollster extraordinaire and political historian Joe Lenski of Edison Research passes along the following:

The only times previous to yesterday that Pennsylvania has been represented by two Democrats in the U.S. Senate have been:

• January 3, 1945 – January 3, 1947 – Francis Myers and Joseph Guffey
• January 14, 1856 – March 3, 1857 – Richard Brodhead and William Bigler
• March 13, 1845 – March 3, 1849 – Simon Cameron and Daniel Sturgeon
• January 14, 1840 – March 5, 1845 – James Buchanan and Daniel Sturgeon

So basically in the last 152 years, the Democrats have held both Pennsylvania Senate seats for a total of two years.

The Republican Party was founded in 1854. So Democrats have held both seats for just three years since the GOP's founding.