Pretty weak excuse. Be prepared, know everything that you said before, and speak calmly and candidly, and admit when you made mistakes, or have changed your mind, and explain why. It's not hard really. I doubt the White House instructed him to be "unfocused" for example per the article. I admit I did not watch the hearings, so my comments are all derivative.
The Pubs might really privately want Hagel to be Secretary, because they think he will be ineffective, and a punching bag. And that might be privately what the Dems are worried about, some of them. It is an interesting dynamic.
Hagel wasn't even that bad at the hearing...the only reason people think so is because Fox News started that talking point and the media - expectedly - parroted it. Hagel's answers were reasonable and yn controversial. It's the Republicans making it controversial and the Democrats - always happy to oblige - who lay down and took it.