What does this all mean for the 2020 Republican Senate election, and the future of our national politics? If you look at the maps of South Carolina in the 2010s, it begins to blur into a mass of blue. The Jacksonians finally left the Democratic Party in response to the Obama presidency, blurring the geographic distinctions in the state. In 2016, Donald Trump won handily — but he barely carried Beaufort County (Hilton Head) and lost Charleston County.

This created a headache for Graham. He was always vulnerable to a primary challenge, but with the state Republican Party increasingly filled with populists from the hill country, his position became dire. With the state seemingly locked up for Republicans, it made sense for him to take positions that would appeal to these voters. Hence his more or less lockstep movement with the Trump presidency.

But this came with its own price. Trump proved unpopular with establishment Republicans, and so the low country moved toward Democrats. It initially appeared that the 2018 victory of Joe Cunningham in the 1st Congressional District – which Mitt Romney carried by 18 percentage points – was a fluke. Trump may still carry the district and Cunningham may still lose his reelection bid, but the movement of this group of voters against Republicans has given Jaime Harrison, Graham’s opponent, a chance in a state that was the cornerstone of the Republican realignment in the Deep South.

What does this mean for national politics? It illustrates what I consider one the fundamental keys to understanding political coalitions: They are like water balloons. When you step on one side, the other side pops up, and sometimes it bursts.