During Tuesday's Democratic debate, Sanders said:
I think the secretary is right. And that is that the American people are sick and tired of hearing about your damn emails. … The middle class, Anderson [Cooper], let me say something about the media as well. I go around the country, talk to a whole lot of people. Middle class in this country is collapsing. We have 27 million people living in poverty. We have massive wealth and inequality. It's cost us millions of decent jobs. The American people want to know whether we're going to have a democracy as a as a result. Enough of the emails. Let's talk about the real issues facing America.
This answer obviously plays well with Democrats, who by and large feel that the email issue has taken up far too much attention compared with issues like the economy and income inequality.
Obviously, this answer wouldn't work as well for a Republican audience. They genuinely believe Clinton can't be trusted. So to them, Clinton's use of a private email server as secretary of state seems like yet another attempt to avoid public accountability while she was in office.
To that end, the email issue very likely won't change anyone's mind about Clinton. If you already don't like her, it'll probably confirm all the bad things you think about her. But if you're open to voting for Clinton, the email discussion looks more like desperate political posturing that distracts from the real issues.