The main difference lies in the fact that totalitarian rulers have marked restrictions on freedoms and the state exercises all power without divisions or restrictions, rulers as Stalin and Hitler are considered totalitarian; The democratic ruler is subject to the decisions of the people that are taken through mechanisms, either direct or indirect, so we can see a democratic ruler in Donald Trump.
Democrats favored expansion in order to increase their power in Congress and expand slavery; Whigs opposed expansion because they feared losing power in Congress.