The Democratic primary debates in Miami were the first of many opportunities presidential candidates will use to make themselves appealing to the nation. Since last week, Senators Kamala Harris, Elizabeth Warren, and former Obama administration secretary Julian Castro have seen increases in their approval ratings.

Chris Lundberg, who is an associate professor of rhetoric at UNC, says these numbers are reflective of their debate performances. He says Warren, Harris and Castro, along with Senator Cory Booker and South Bend, Indiana mayor Pete Buttigieg, all hit the three benchmarks each candidate should aim for: present your biggest message, provide some biographical information and emphasize differences between themselves and the others running.

“The candidates who over-performed in this debate did all three of those things,” says Lundberg. “They talked about their history; they talked about issues relating to policy in reference to their own past; and they did it not just by creating distinction with folks on the other side of the aisle but creating distinctions between themselves.”

In a field of 20 Democrats this election cycle, those distinctions and approaches to highlighting them are crucial. Another way to do this in the debates is to directly attack others, which was part of Harris’ and Castro’s strategies. Lundberg says while this can be risky and make voters uncomfortable, it can be very effective.

“On one hand, they don’t like negative things in politics. They’re worried about them being partisan and divisive,” he says. “On the other hand, negative attacks not only tend to be memorable but tend to distinguish [candidates] from other people. Even if it has some negative effect on your likability, it creates a positive net effect relative to the rest of the field.”

Looking ahead to the election in 2020, Lundberg says he expects whomever wins the Democratic nomination to challenge President Donald Trump in the debates. It will be different from 2016 when Trump had no political record.

“I think President Trump, this time, will not have the advantage of simply being on offense against the political establishment,” says Lundberg. “He’ll have to defend a record, specifically a record that includes a bunch of really difficult [issues], from people on the progressive side but from people on the conservative side too.”

Before then, however, there are still 10 more primary debates scheduled. The second round of Democratic debates in the primary season will be held at the end of this month, on July 30 and 31 in Detroit.

To listen to our full conversation with Chris Lundberg, click here.