Not only is Lewis a lock at left back, he may have become one of the most critical players to the US team after the Gibbs injury. Arena lost a lot of flexibility with that injury. (notice I'm not suggesting he is a great player necessarily).
Bocanegra is a solid player in the middle but will not see any time on the outside. He's too slow and would get eaten up by most wing players. Lewis isn't there for his offense, he's there because he has the experience and speed to defend on the outside. Nobody left on the squad can do that. Let's hope he doesn't get hurt or accumulate cautions. If he does you could see the US have to really mix change things around in order to defend the flanks.
