USA has been playing well in the group, but look at their opponents: Ghana dominated but were poor finishing and Portugal has been pretty terrible for their standards. Germany's aim is to win the group for an easier competitor in the next round. The USA can still qualify if they lose, although it's obvious they will play to at least draw.
This is by far the USA's toughest challenge so far facing the 2nd World Cup favorite according to the oddsmakers, are people afraid of taking Germany because of all the hype around the American's good run so far?