Oh come on. Reagan's landslide victory was surely a mandate.
No, as much as I admire what President Reagan accomplished, his '84 landslide was an affirmation, not a mandate, because of the non-ideological themes of his reelection campaign. Reagan had a true mandate with less votes in 1980 than in 1984 because that campaign was ideological.
Landslides and mandates are not mutually exclusive, but they are two different animals, one arithmetic and the other ideological.