Because political pundits like to be contrarian on mornings like this, they'll unleash one of their old standbys, like, "Well, you know, Steve Doocy, 98 percent of incumbents are going to get re-elected. So it's really not correct to say that this is an anti-establishment, anti-incumbent cycle."
That line is content-less. It's like saying that your record as a political prognosticator is excellent because you correctly picked the winner of 400 of 435 House races. Actually, only about 35 (or 70) House races need prognosticators.
In places where the political environment allows for a competitive race, it SURE AS HELL is an anti-incumbent, anti-establishment year. It is many more things, too, but don't fall for that bit of punditry tomfoolery.