In the 1930s FDR attempted to throw control of SCOTUS into long term Democratic control by adding additional numbers of members to the Court via legislation, as the exact make-up of the Court is not defined by the Constitution. What if Trump attempted to do the same thing, adding say four more seats and populating them with young, conservative justices. Conservatism could have an unassailable majority for multiple decades.

https://en.wikipedia.org/wiki/Judicial_Procedures_Reform_Bill_of_1937