I'm actually really interested to see how Clinton responds to this going public.
I think that there's a clearly right strategy here, and I think her first instinct is going to be very wrong. A major lesson from modern politics, and one that Donald Trump has learned really well, is that you should never apologize or admit to being wrong. About all sorts of things. It doesn't help, except maybe as part of a multi-year process of reinventing a political persona. People who think that what you did or said disqualifies you are validated by your apology. Your most strident defenders have to switch gears from insisting that you did nothing wrong to acknowledging that you're a monster but you apologized so can't we please drop it?
Something that's hurting Clinton more than anything else in this campaign is that she apologized for the email thing. She'd be much better off now if she'd just insisted from the start that she'd fully complied with the law, had done what she had to do to be an effective SoS, and anyway this is perfectly normal for Secretaries of State (like Colin Powell). Does anyone think that her apologizing for the email thing has been good for her? Now it gets brought up every time the press has a chance to ask her questions and every story is free to assume that it's a big problem. Matt Lauer opened the veterans' forum the other day by asking why the email thing was not "disqualifying". That is not a question a candidate wants to be answering.
Meanwhile Trump gives voice to overt racism five times before breakfast and also commits some fraud and bribery and no one really cares. Why not? I think a big part of it is that he's made the question of whether or not what he said and did was wrong a partisan one. There's no continuing news hook here. You can't badger Trump about Trump University because all you're going to get from him is that you're lying scum for bringing it up, and his supporters will cheer.
So I think that there's a right strategy from Clinton here, and it's to double down. Admit that it might not be the most politically correct thing to say - imply that she's a lot harsher about Trump and Trump supporters in private - but talk about the importance of honestly confronting the problem. This is easy stuff. Just go look for a Republican statement on the importance of using "radical Islamic terrorism" and find-and-replace. Talk about how Republicans like Paul Ryan clearly agree with you but are too scared to say it. Blame the media for being so obsessed with finding the truth in the middle that they end up following Donald Trump as he runs to the right.
People really like it when politicians perform a willingness to offend other people that they don't like.