mean1 <- 0.21
mean2 <- 0,36

all <- data.frame(Who = c('Trump', 'Clinton'), Value = c(mean1, mean2))
all

all %>% ggplot(aes(x = Who,
        y = Value,
        fill = Who)) +   # here is the trick

  geom_histogram(stat= 'identity',  position = 'dodge') +

  theme_bw(base_size = 10) +

  labs(x = "Year", y = "Negative proportion")