Federally mandated cooling-off period ends Friday, opening possibility of nationwide strike or lockoutA national railroad strike could derail critical deliveries of chlorine to wastewater treatment plants and coal to utility plants, among other potentially crippling disruptions, prompting senior White House aides on Tuesday to review contingency options for protecting the nation’s drinking water and energy supply.White House aides are looking at how to ensure essential products carried by rail — such as food, energy and key health products — could still reach their destinations, even in the event of a strike. Senior officials have looked at how highways, ports and...