A natural reaction from American voters following the Watergate? Also remember that leftism was very fashionable in the 1970s - it was at its height of influence on all fronts (at least today economic leftism is on the retreat) and free market beliefs were confined to "eccentric" individuals like Milton Friedman, Pinochet-era Chilean economic ministers, or colonial Hong Kong civil servants.
Nonetheless, even with this set of factors Carter had to campaign emphasising he was no leftist, and even under this set of condition Gerald Ford almost pulled a victory. It just shows that full-frontal leftism has less market in America than Britain or any Western European country for instance.
Carter lied about everything.
I especially remember Time Magazine publishing something to the effect that we would never beat the Soviets, that all we could do would be to delay their eventual victory over the West while we tried to negotiate a temporary peace.
Thank the Lord for Ronald Wilson Reagan.