Though Casey still holds a lead on Republican challenger Tom Smith in every independent poll, Smith has managed to keep that lead to single-digits, and in some cases, within the margin of error. Majority PAC's move is an indication that Democrats are beginning to grow worried about their prospects in the state.

The ad highlights what it characterizes as Casey's votes to increase education funding and to make college loans more affordable, while attacking "tea party Tom Smith" for his position to eliminate the Department of Education.

The PAC, which aims to protect the Democratic majority in the Senate, also launched ads in Indiana targeting Richard Mourdock, in Nevada against Sen. Dean HellerDean Arthur Heller20 weeks out from midterms, Dems and GOP brace for surprises Trump to attend fundraiser for Heller Dems seek to seize on data privacy as midterm issue MORE and in North Dakota hitting Rep. Rick Berg. 

Watch the Casey ad: