A Senate Republican super PAC aligned with Minority Leader Mitch McConnell is pouring $67.5 million into close races in Pennsylvania, Wisconsin and Michigan to tear down Democrats’ “blue wall.” With less than 35 days until the election, the Senate Republican Leadership Fund is shelling out for TV, radio and digital ads targeting Sens. Bob Casey (D-Pa.), Tammy Baldwin (D-Wis.) as well as an open seat left by retiring Sen. Debbie Stabenow (D-Mich.). The largest sum, $28 million, will be funneled into Pennsylvania, where GOP Senate candidate Dave McCormick has closed the polling gap to within the margin of error against Casey in…