The national Democratic Party has added the Congressional District 15 seat in Hillsborough, Polk and Lake counties to its "Red to Blue" list of districts where it believes it has a strong chance of taking over a Republican seat.

The move follows release of an internal campaign poll showing Democratic Kristen Carlson statistically tied in the race with Republican state Rep. Ross Spano. The poll commissioned by the Carlson campaign from a national Democratic political polling firm showed her one point ahead, 48-47 percent, with a 4.9-point error margin.

U.S. Rep. Dennis Ross, R-Lakeland, is retiring from the seat.

Congressional District 15 becomes one of 82 districts on the Red to Blue list nationally, one of five in Florida, and the second to include part of Hillsborough County.

Also on the list is District 16 covering parts of Hillsborough, Manatee and Sarasota, where incumbent Republican Vern Buchanan faces Democratic challenger David Shapiro.

Amanda Sherman of the Democratic Congressional Campaign Committee, the party's U.S. House campaign arm, said criteria for the list include indications of local support, campaign organization, fundraising and "aggressive goals for grassroots support."

Once on the list, a Democratic candidate can expect to receive campaigning and fundraising advice and assistance and possibly direct financial contributions, Sherman said.

"It means national Democrats have recognized this as one of the most flippable seats in the nation," said Carlson campaign manager Conor Hurley.