Does everyone think critically and rationally? If not how many don't (especially during key election periods) and can this group cast an oversized influence on

Does everyone think critically and rationally? If not how many don't (especially during key election periods) and can this group cast an oversized influence on election results or public opinion? Having the choice of two options at the ballot box, and social media meaning many people now form political opinions from anonymous accounts online does not fill me with confidence.