By Simone Pathé and Bian Elkhatib

Senior political reporter Simone Pathé breaks down the changes in Roll Call’s list of the 10 most vulnerable lawmakers in each chamber. Sen. Bill Nelson, D-Fla., moved up on the list after Florida Governor Rick Scott entered the race, and Rep. Rod Blum, R-Iowa., moved up after Rep. Darrell Issa, R-Calif., announced he would not be seeking re-election.