The conventional wisdom is often wrong. Crime didn't keep soaring in the 1990s, money alone doesn't win elections, and - surprise - drinking eight glasses of water a day has never actually been shown to do a thing for your health. Conventional wisdom is often shoddily formed and devilishly difficult to see through, but it can be done.
Do I think that American democracy ends if Trump is president? No! I think, there are plenty of checks and balances in place. I think he would do some damage to the country but we would recover. The office of the presidency and American democratic institutions are a lot stronger than one person. So if he wins, our job is just to keep the office strong, right? And hope he'll be replaced by something better!