A few weeks ago, GOP presidential hopefuls were asked: "if you knew then what you know what, would you invade Iraq?"
In principle, there are roughly four different answers you can give:
i) A libertarian like Rand Paul would reformulate the question: "Given what I knew then, I opposed the war!"
That would invite a follow-up question: "So why did you think it was wrong at the time?"
ii) The respondent could challenge the question: presidents don't have the benefit of hindsight. They must make important decisions based on the information they have at the time.
iii) A respondent could say "no."
That would invite a follow-up question: "So what do we know now which leads you to believe the invasion was a mistake?"
iv) A respondent could say "Yes, but…"
In other words, he could say it was still the right thing to do, but we should learn from our mistakes. If we had it to do over again, we should change the strategic objective and/or the tactics.
That would invite a follow-up question regarding the alternative strategy and tactics.