The quote above comes from the Gettysburg Address, not the Constitution. We are a Republic. We select our government and they make decisions on our behalf. They dont necessarily do our bidding, nor were they created to do so. They are supposed to use their judgement and do what is best for the country, not just take the latest poll numbers and turn them into policy.
Governments must give presumption of innocence in the way they treat prisoners. The lay public does not have to and if you watch any TV, you know they dont. Most have a pretty good idea of guilt prior to any trial. I surprised we can find any one who doesnt have a preconceived idea or is willing to weigh the evidence.