Mostly through their decisions concerning the economics. During his presidency, Reagan reduced taxes,transferred some resources and credentials to state governments, bounded the regulatory activities of federal agencies, and assigned conservative adherents to federal courts. Bush senior has continued the policy of his predecessor. Basically, they’ve enabled monopolization within the most productive sectors, while made the rules harsher for small businesses. The course taken by Reagan and Bush was continued by Clinton.
That’s not a question of a couple sentences. You’d better look up analytic materials. I’ve found here a paper identical to your question.