Remember when Barry Goldwater lost in a blowout election and forced Republicans to put up the ultra liberal Richard Nixon in the next cycle?
To be fair, Richard Nixon was to the left of any major Republican Party leader since Reagan. Had Kennedy not fucked up the USA would have had a better healthcare system 40 years ago. Nixon was a deeply corrupt, unpleasant person, but in policy terms the Republican Party wouldn't let him in nowadays.
Lesson for Sanders fans there - Nixon offered healthcare reforms. Kennedy refused because it wasn't everything he wanted, which then killed healthcare reform for 40 years. Perfect can absolutely be the enemy of good.