The venom with which she spewed at Trump with her first question underscores his point. Her goal was to set the tone for the media treatment of him and his campaign, if not take him out in a matter of hours.
Trump’s answer (”Only Rosie O’Donnell”) totally defused that whole character assassination attempt by making a joke of it. And let’s face it, from that comment everyone’s mind was picturing Rosie and thinking “well, he had a point” instead of some poor struggling single moms like Megyn wanted them to.