Semistable abelian varieties over $\mathbb{Q}$ with bad reduction at 19 only

We classify semistable abelian varieties over $\mathbb{Q}$ with bad reduction at exactly 19 up to isogeny over $\mathbb{Q}$. The general strategy goes back to Fontaine and has been heavily refined by Schoof. In the beginning of this paper we include an overview of this strategy, proving various non-trivial background results along the way, as an introduction for readers unacquainted with this topic.