Reagan's las slide victory in the presidential election of 1980 proved that

Reagan's las slide victory in the presidential election of 1980 proved that Americans were ready for a change in leadership after defeating incumbent Jimmy Carter and this was due to dissatisfaction with Carter over worsening economy.

(See explanation below for further details).

Explanation:

Political, social and economic conservadurism and religion has a big influence on a wide sector of US society, in contrast with a more secularized vision held by liberals, progressives and socialists, ideas which were associated with the Democratic Party and the criticized administration of James Carter as US President.