I´m not sure "stupid" would be the exact term, rather liberals see conservatives as more as assholes in the sense of the racist, sexist, bigoted, religious, jerky, selfish, money-is-god, loud mouth, angry, hypocritical, militaristic personality that is perfectly demonstrated by Señor Trump and his high poll numbers. Although yes, you also do see the mouth breather "stupid" type Fox News Republican true believers en masse.
I would say a majority of the crafty, sly "intelligent" well-to-do, decent Republicans (the "establishment") are not happy that Trump is unapologetically voicing some very unpopular core values of the modern American Republican conservative without filter and without the politically correct muzzle, and want him out of the race for obvious reasons.