Kos poll: Burns by six By: Josh Kraushaar April 30, 2010 12:59 PM EDT Weighed down in his district by low presidential favorability ratings and a health care law that's unpopular there, Pennsylvania Democrat Mark Critz now trails by six points in next month's special election for the seat of the late Rep. John Murtha, according to a Daily Kos/Research 2000 poll released Friday. Critz, who served on Murtha's staff before the congressman's death, takes 40 percent of the vote in the poll compared with 46 percent for Republican businessman Tim Burns. The poll shows President Barack Obama's favorability number...