Even though the US's aid agreement stipulates they stop sending aid in the event of a coup, that is exactly what happened in Egypt and the government continues to send aid. How can you be called credible after that? When you support a military regime performing a coup and killing the protesters and beyond that, send them aid?
The previous and current upheaval in Egypt is an example of a society going through political turmoil. There are a lot of cultural and political aspects that go into the revolution of Egypt, but neither of these factors damage the credibility of the United States. The US can choose to help or not help Egypt, but it says nothing about their credibility.
Egypt crisis is not damaging America's credibility because we chose to go over there and help them out and we have the opportunity to say know or know what will help us or hurt. Also I believe that it is better to give than to recieve because then you will be more of a affect on people's lives.