The National Republican Congressional Committee is up on radio airwaves with a spot blasting Bethlehem Mayor John Callahan (D), who announced earlier this year that he is challenging Rep. Charlie Dent (R) in the eastern Pennsylvania 15th district.

The NRCC would not divulge the size of the buy, but their early purchase signifies that this is likely to be one of the top targeted races of the 2010 cycle. The radio spot, “It’s a Callahan Christmas,” follows Dent’s 10,000 robocall “offensive” against Callahan earlier this month.

CQ Politics currently rates the general election contest in Pennsylvania’s 15th district as Leans Republican.