A lot of the reason she won is because of her introduction video which, as the saying goes, went viral. She raised $2 million off of it. It's absolutely great -- one of the best political campaign videos I've seen. I retweeted it around, though I was in good company.
I'm biased in part because she refers to her mother being a polio survivor. My mother was too, and lived to the age of 87. But I was taken by Ms. McGrath's video long before she even got to that point. It was just icing on the cake. But in recent perspective it's all the better -- remember how on just this past Monday I hoped that Democrats would remind voters about the importance of the Affordable Care Act and how Republicans voted to gut it? Well, that's precisely what Amy McGrath did in the ad (and I'm sure in her campaign), which is why she brings up her mother.
But watching only the video, I suspect that even from seeing that little, it's likely she won the Democratic primary for a lot of reasons, not just that one thing.
The seat is currently held by a Republican, Andy Barr. But it's considered winnable by Democrats. Barr won his most recent election by 22 points. However, it's not a Deep Red district. I believe that Trump won it by only five points. Four years earlier, Mitt Romney only won the district by eight points. (Which also means it got closer...) And more to the point, in 2010 the district elected a Democratic congressman. One other issue, something I talk about regularly which I think will be a major factor in the mid-terms: the Enthusiasm Gap. In fairness, the Republican candidate was an incumbent, but he did have a challenger. 48,372 votes were cast in the Republican primary. The Democratic primary had 100,418 votes cast.
And as for seeing -- here's that video.