Why is the country only 42% Democratic ?

[Spider Jerusalem]

20. 42% isn't low

it's a larger proportion of the registered voting population than the GOP. And it's about the most you can expect in a two-party system that allows registering as an independent. Although one source I found put the percentage of registered voters identifying as Democrats at 34% vs 28% for Republicans, which means independents or other parties make up 38% and more than either.

And as far as the American people and their beliefs: according to various polls from credible organisations, 46% of Americans have a creationist view of the cosmos and believe the world is 6000 years old; 33% of Americans believe the Bible is the literal word of god, 77% believe in the existence of angels; more than 40 percent believe in the millenarial evangelical Rapture, about 40% believe they're in the top 10% of income earners. And close to 100% of the American working class believe they're actually "middle class" because their politicians have been lying to them and telling them they are for generations. (Because genuine class consciousness breeds socialism which is un-American, don't you know.)

Americans are by and large the most ignorant, religiously fanatical, backwards, and insular people in the developed world. If the Republicans communicate better it's because they craft their messaging to appeal to base emotions rather than reason. Simple formula, use words like "security" and "freedom" along with pictures of eagles and flags and soldiers in uniform, bonus points for associating your Democratic opponent with Communists, terrorists, atheists and queers. You can't fight emotion with logic, it doesn't work.