I wouldn't be so naive as to take Oprah's running for granted.
Remember, in 2008, the US elected a guy with 0 resume and god awful liberal statements and positions all over the place- all because he was 'historic' and could put two sentences together. In 2016, we elected someone because he could play the media and could 'fight' (and because he ran against the worst candidate since Walter Mondale). In both cases, one could say the voters were 'hoping for change'.
Oprah owns (no pun intended) a media empire, could be considered 'historic', can string two words together without sticking her foot in her mouth, and is loved by the often ignored middle. She is also a self-made billionaire (almost the same net worth as Trump, 3.5 versus 3.7 Billion) who doesn't have financial baggage (no bankruptcies or bailouts). She isn't considered old, nor is she considered controversial outside the entrenched base in either major party (who won't shift anyway, no matter what is thrown at them).
Demographics are also changing rapidly. Millennials just overtook Baby Boomers as the largest voting base*- the same Millennials Rush is fond of mocking and acts like they aren't needed. He is very naïve in his attitude toward them. Boomers, on the other hand, who Conservatives usually rely on, are dying off quickly**. Millennials are socially liberal/libertarian and don't have a lot of love for traditional social conservatives of the 'religious right' type***. They could be swung towards limited government, 'classic liberal' thinking but the Conservative base has been moving towards a stronger centralized government they can use as a hammer and away from limited government.
We can add a few more things to this pile. There will eventually become 'trolling fatigue'. We already started to see this with the Roy Moore/Doug Jones battle where many on the right were just tired of the whole thing and chose write-ins over checking the box for the Republicans- enough write-ins to throw the election in what normally would be a strong Conservative foothold.
On top of that, if Oprah makes it clear, even behind back room doors, that she is running, you will have an all out image push by the media, from the old media to new social media, to push her image and craft her into their ideal candidate. She, like Trump, will bring in a new way of campaigning. But I suspect, unlike Trump, she will not try to alienate and fight opponents but win everyone over with flowery speeches and rhetoric.
The further the pendulum swings one way, the further it will swing the other way and so on and so on.
Republicans and Populists need to wake up and realize the high they are on now can't last. It never does. (just like the Obama high didn't last for Democrats)... History shows us this.
*
http://www.cnn.com/2017/07/25/politics/brownstein-millennials-largest-voter-group-baby-boomers/index.html**
http://www.fortmorgantimes.com/ci_20010202***
http://reason.com/poll/2014/07/17/millennials-are-social-liberals-fiscal-c
