Well, US was in the Civil War at the time. Also I'm not sure how something that happened 150 years ago is relevant now.
It isn't relevant. Nor was Abraham Lincoln an 'arch-conservative', especially by the standards of the day. Nor was his suspension of Habeas Corpus unconstitutional if you're in the camp that the war he lead on the south was against a rebellion, and not an act of aggression.
That said, in modern times, very few politicians at the national level respect and appreciate the U.S. Constitution, and it's likely that almost as few have even read it. Something that most of even the worst politicians at the national level in the 19th century had, and had done.
Is it actually possible to graduate from school in USA without getting passing grade from course about constitution? (Not any way relating in topic, but I am just curios)
You're talking about a country where random Joe doesn't even know all 51 states.