Reagan had a mandate, could have gone for: 1- immigration restriction (2015-16 MAGA line) 2- neutral (2000s-2010s mainstream R line) 3- soft line, lax enforcement, limited rhetoric, outright amnesty. He chose 3. See also "Ronald Reagan" section here:https://hailtoyou.wordpress.com/2019/11/04/the-decline-of-california-when-and-why/#wholostcalifornia …
Reagan didn't have a "mandate" he had a big electoral win, no win condition and an infinite number of ways to lose. Whichever area he made a mistake in would have destroyed the country. The left of those days was desperate for a merger with the Soviet Union