Would it be fair to ask Scott Walker whether, knowing what we know today, he would have ordered the invasion of Iraq? Of course it would. Walker could point out that he was the County Executive of Milwaukee at the time — ordering war in Iraq was not in his portfolio — but that now, in retrospect, knowing there were no weapons of mass destruction, he would not have authorized the invasion. End of story.

The same for Rand Paul, who was an ophthalmologist in Bowling Green, Ky.; for Marco Rubio, who was a member of the Florida House of Representatives; for Mike Huckabee, who was the governor of Arkansas; and so on through the Republican 2016 field.