Let's be honest. Oprah has a definite appeal across traditional party lines, just as Donald Trump demonstrated when he shattered Hillary's once-thought-to-be-secure "blue wall" in Michigan, Ohio, Wisconsin, and Pennsylvania. She could be a formidable candidate, but remember: Donald Trump had to overcome sixteen other Republican candidates. The party regulars and presidential wannabes did not meekly surrender, and we doubt if the Democrats will do so either. Particularly one woman for whom 2020 might be her last chance (of many). Perhaps the biggest hurdle that Oprah will face is that the Democrats who want to be president are unlikely to stand aside and defer to her. That includes Hillary Clinton, who wants one more try to win the Oval Office. We don't see her folding her hand before all of the cards are dealt.
This cross-party appeal is a key to victory. The "Reagan Democrats" were a vital part of his coalition, and both Bill Clinton and Barack Obama began their quests for the presidency by being critical of their own party's doctrine and aiming for some common ground with the other party. That may have been more an electoral ploy than a sincere outreach, but it helped to give them favorable attention for not being "just another liberal" and gave them a solid footing for their election campaigns.
Anyway, Oprah and Donald Trump have so much in common that it isn't hard to imagine that she also could make a successful run for the presidency. Perhaps this type of campaign is needed to break the hold of the professional politician.