Trump has spent a couple of decades talking about what he believes. Most of it is in his books. As I understand, he's written over half a dozen.
No, Trump didn't spend the last four to six years traversing the country, speaking to audiences, as Reagan did before 1980, but his thoughts and positions on issues and politics are well known.
As for Reagan...I was thinking of his time as spokesman for GE, before his Governor gig.