These results suggest that the most effective Democratic challenger to President Trump in 2020 would invoke conservative values while offering progressive economic policies.
I think that makes sense. Though the candidate shouldn't use "conservative"; he should, however, make occasional reference to "traditional American values". It just might work. After all, Trumpty calls himself a "conservative" even though he isn't one.
And the authors are right to say the candidate who best represents what they suggest is Mayor Pete.