Mondale, while having the label as an "Old Democrat", made this line over and over like a broken record:
Tax cuts for the wealthy will erode the middle class and lead to disproportionality of wealth and power (paraphrased).
Back in '84, people laughed at him. Look where we are now folks.
Actually, the polling at the time suggested the vast majority of Americans agreed with him, but for many it wasn't enough to shift their votes. Lots of cognitive dissonance in 1984.
Actually the American people made the right decision in that eleciton