Learn English – What does “growing from strength to strength” mean

The Mandela quote is in a different context i feel. “It is better to lead from behind and to put others in front, especially when you celebrate victory when nice things occur. You take the front line when there is danger. Then people will appreciate your leadership.” Mandela here is definitely saying that Leading from Behind means that the leader should step back when the group or organisation or nation is celebrating something and step in to the front only when there is need for him/her to lead from the front.

So if we refer to Mandela's quote, then what Obama's statement means is quite remarkable. It would mean that the US won't get involved in the Libya issue but will be there to take credit by staying behind the scenes if things get better.

Another way to look at it would be that it was a diplomatic sort of a response to the matter at hand. Obama washed all responsibility off his hands in a manner of speaking.

The phrase "eat our peas" is not, as far as I know, a historical metaphor. However, according to the context given by CBS, President Obama was telling the nation that they had to buckle down and do what might hurt but would be good for them.

To add further context and explanation, the sentence also referred to "pulling off the Band-Aid". When you need to take off a Band-Aid, you have to rip it off in order to get it over with. The president was saying the same thing twice.

Edit: There is more discussion of this metaphor here, as it is not a usually accepted metaphor. The author writes,

I take it that the pea-eating metaphor is intended to indicate that all sides must take an unpleasant political hit to settle the debt issue. They won't like it, but it'll be good for them.