Answer
Tell me a national leader that is both strong and experienced that has actually performed well for the country recently.
Easy one: Bill Clinton. He had way more experience in his first run than Obama, and immeasurably more his second run.
My guess is Obama appears weak because he's had to absorb so many groundless attacks over and over. I think that would wear on anyone.
So appearing weak is okay or even good???
I have never seen a political bloodbath on the scale of the New York Primary in 92. Bill Clinton fought his was through personal attacks that would make 99% of politicians tuck tail and run.