• US citizens could take it as insult, when a potential American president doesn't speak about "America has to lead", but in terms of following (see e.g. the flag pin debate on how sensitive Americans can react on issues, which can be interpreted critically towards them) // In any case he is not yet US president. So in a way his prime audience is still the US voter.
  
• if he just wants to make his German and European followers happy, the KumbayObama (as you called it) will do it perfectly well. I think he can't do much to alienate them, except speaking about Afghanistan. So no need to alienate his voters at home.
  

i don't need him to be too humble, lol, but simply for him to accent unity and good faith in the same way he does back home.

he has a lot of savvy, i expect he'll finesse this ok.

The person who says it cannot be done should not interrupt the person doing it. Chinese Proverb.