in wall to wall tonight, an update on the effort to cap that tragic oil spill in the gulf of mexico. we want to show you this structure right here. it looks a little awkward, but it left port today. it's a giant dome, a cap they want to use to plug the biggest leak underground. they capped the small one today. let's show you how this is supposed to work. here it is right here. it will be brought out on a crane. the idea is to lower it down over where the oil is gushing out. if it is successful, the oil would be taken in a tube to a tanker ship. that is a plan. still questions about the engineering of this would work. let's walk over to the magic wall. a big political debate about the pace of the disaster response, whether bp has been forth coming, let's go back and look at the key days. it was on the 20th of april that the oil rig exploded. search and rescue was the top priority in those first days.