Sen. Bob Casey Jr. (D-Pa.) has a double-digit lead over Republican Tom Smith, according to an internal poll released by Casey's campaign.

The first-term senator leads Smith by 52 to 39 percent, according to the poll. Internal polls should be taken with a grain of salt, and Smith's own internal poll has him within a few points of Casey. Recent public polls have varied widely on how competitive the race is, with three recent polls showing Smith within 2 points of Casey in the state and two others showing the senator with a double-digit lead.

Republicans have been talking up the race as the sleeper of the election, and some Democrats, including former Pennsylvania Gov. Ed Rendell, have said Casey has given Smith an opening by not campaigning hard enough and by allowing the wealthy coal mine owner to heavily outspend him on ads.

But most Democrats believe the senator will be fine in the end, and the race has yet to emerge as a top priority for national Republican groups, though Smith's ability to self-fund lessens their need to get involved.