One big question about 2020 is whether President Trump will face a serious primary challenger for the Republican presidential nomination. …
In the modern presidential primary era, three incumbents have experienced what we’d consider a serious primary challenge: Gerald Ford, Jimmy Carter and George H.W. Bush. And in all three cases, the incumbent lost the general election. Now, to be clear, it wasn’t necessarily because they faced a primary challenger — instead, it’s better to think of a serious primary challenger as a canary in the electoral coal mine, a sign of an incumbent’s vulnerability.
So we built a rough “Primary Challenge Success-O-Meter” that looks at primary challengers from the past to better gauge how 2020 challengers could rate. CONT.
Geoffrey Skelley, FiveThirtyEight