His socially conservative positions and populist rhetoric.
^^^
One thing I have always thought was fascinating about Reagan was that he spent as much of his time criticizing policies created by the Supreme Court as he did criticizing policies created by Democrats in Congress. He supported public school prayer, which meant he was critical of
Engel v. Vitale. He opposed bussing, which meant he was critical of
Swann v. Charlotte-Mecklenburg Bd of Educ. He opposed abortion, which meant he was critical of
Roe v. Wade. These were the kinds of issues that appealed to many Democrats.