Jim Geraghty of National Review Online warns Trump supporters against overconfidence about the president’s re-election.

Trump, his campaign, and his supporters probably shouldn’t get either too confident or too gloomy. It’s worth keeping in mind that despite Trump’s comfortable Electoral College margin of victory in 2016, and Hillary Clinton’s popular vote margin of nearly 3 million votes, the margins within many of the key states were razor-thin — the sort of situation where neither party should be brimming with confidence about keeping the state in 2020. The last presidential race had four states where the margin of victory was less than one percentage point and another six states where the margin of victory was less than four percentage points.

The big three that decided the election were Michigan (where Trump won by 10,704 votes) Wisconsin (where he won by 22,748 votes) and Pennsylvania (44,292 votes). As many have observed since the final tally in 2016, this means about 77,744 Americans made the difference in that election. For perspective, the average home attendance of the Michigan Wolverines last season was 110,736.

In other words, if Democrats can add less than a full football stadium’s worth of votes to Hillary Clinton’s total in those three states in the right proportion, they’ll win the presidency. And for what it’s worth, his approval rating in those three key states is currently in the low-to-mid 40s and he’s losing head-to-head matchups with Joe Biden in these states by a wide margin.

But a lot of the discussion around 2020 is overlooking a bunch of other states that should be considered jump balls.

The 2020 Democratic nominee could outpace Hillary Clinton’s vote total in one or more of the other not-quite-as-red-as-it-used-to-be states, just enough to flip them. Trump won Arizona by 91,234 votes, Florida by 112,911 votes, Iowa by 147,314 votes and North Carolina by 173,315 votes. (That sum may sound like a lot, but it amounts to just 3.6 percentage points.)