McGovern's floor was significantly lower than usual, at least in part, because his opponent was no conservative. There were any number of progressively inclined voters who voted for Nixon but could not vote for Ronald Reagan eight years later. Nixon (Mr. wage and price controls, affirmative action and detente) was part of the progressive Republican tradition and he had a broader potential constituency than any candidate contemporary conservatives would tolerate. Carter would have done better without John Anderson who got 6% by drawing people who loathed Carter but couldn't stomach a conservative. Mondale lagged a bit behind the normal rock bottom because of special circumstances (he was a hopeless politician and RR was himself).
All in all 42% is a pretty good estimate of the proportion of voters no conservative can reach barring truly extraordinary circumstances.
By the economy alone, we live in interesting times. Thanks for replying.
From which we conclude what?
"Come to Daddy, you conservatives -- give it up, and come and lick the hands of your betters!!"
Something like that, what you had in mind? Mittens, I bet.