It can be hard to remember this now, but Donald Trump actually ran as a relatively moderate Republican on most of the issues. The substance of his campaign, of course, was overwhelmed by the violence of his rhetoric on immigration, crime, and foreign policy, and his white nationalist base responded as he planned; hence, his famous comment that he could shoot someone on 5th Avenue without losing his voters.
There is a bit of a lesson in his success for the Democrats in 2020. The current assumption is that only a fundi who promises the moon and stars on spending programs will be able to inspire the base, but that isn’t necessarily correct. It will be perfectly possible to sell a sensible center-left program to primary voters as long as the candidate opposes Trump and Trumpism in a colorful, memorable way.
In short, substance matters, but so does style.