I've removed the original post of a little time ago because after listening to the clip about two dozen times, what sounded like McCain saying "horseshit" actually comes through as having a hard "c" at the front of it. My husband insists that McCain said "Course not." I think now my hubby's right, although it's very muffled. You can hear the moment at around the 4:30 mark in this video. I'm sorry for mis-hearing this. I've heard McCain say worse in my presence (and thought none the less of him for it) so it wasn't exactly bizarre.
[Update: a reader persuasively says that McCain is saying "'Course you can" and it sounds like "corshucan".]
[Update II: I just listened to it all over again and now I'm not clear again. Oh, the joys of blogging in real time. If anyone has another translation for what was an under-the-breath remark by McCain, I'd be happy to air anything that makes sense. I'd email the McCain campaign but they won't answer blogger emails.]
[Update III: I listened to it on headphones. Now I think my husband was right again. McCain says: "'Course ... Course not." Well: 'mutters angrily' conveys the tone better.]