Where is the Constitutional foundation for .....?

What Constitutional foundation is there for "I am my brother's keeper...."? as Candidate Obama proclaimed in his DNC speech.

I just don't see it in the Constitution.

I'm not saying that it's un-constitutional. I'm just saying that I don't see the Federal government's role spelled out in the Constitution to be: "Sure I'll take care of all of you." as was implied by that statement by the now President.

Here we go........................hold on for the ride :)