The Issue: the vote to authorize the use of force in Iraq
The Question to H. Clinton: "Was it a mistake ?"
The Answer: H. Clinton explained the context at the time but did not say it was a mistake. She basically said that she had no idea that Bush would use that vote to go to war.
The reply by B. Obama: acknowledging that H. Clinton had a lot of experience, he also said that the vote was clearly about giving the authorization to Bush to go to war. And then he added that the next President: " Need to be right on day one" - a reference to Clinton's line about being ready on day one.
Bottom Line: There are many nuances lost in that debate which would make one understand Clinton's vote. For most Americans who disapprove the war now, she is definitively on the wrong side on this one.