President Trump is in office because of 78,000 voters in three states. His narrow margins in Michigan, Pennsylvania and Wisconsin were enough to flip those states from blue to red in 2016, and those flips were enough to give him the electoral votes he needed to win the presidency.

That narrow margin, though, means any number of small shifts away from him might have resulted in Hillary Clinton winning the election. Any one of thousands of things — no last-minute announcement by former FBI director James B. Comey, more attention paid by Clinton to turnout, and on and on — and suddenly that election potentially looks a lot different.

2020 is a different year with a different opponent and a different context. It still seems safe to assume, though, that Trump’s path to reelection is not a particularly broad one, given his static approval ratings, and, therefore, that he will want to do his best to hold his 2016 support as he seeks a second term. With the general election upon us after Sen. Bernie Sanders (I-Vt.) dropped out of the Democratic primary race on Wednesday, a number of recent polls show Trump’s support in a head-to-head contest against former vice president Joe Biden is lower than it was against Clinton on Election Day four years ago.

Four polls from The Economist-YouGov, CNN-SSRS, Monmouth University and Quinnipiac University — all conducted before Sanders left the race — show Biden with a national lead over Trump. Monmouth has the closest margin, with Biden up four points. CNN’s poll is the widest, with Biden enjoying an 11-point lead. On average, the four polls give Biden an eight-point lead — six points more than the two-point margin by which Trump lost four years ago.

Why that shift? Because a number of demographic groups now show more support for Biden against Trump than they did for Clinton against Trump in the last election.

One of the most notable changes is that eight-point shift toward Biden among women. That overlaps with the huge 25-point shift seen among whites with a college degree; white women with college degrees have shifted dramatically against Trump, helping to power the Democratic takeover of the House in 2018.

But even among whites without a college degree, Biden fares much better. He polls 17 points better against Trump than Clinton did in 2016, according to exit polls. This comports with a central argument of Biden’s primary campaign: that he was the candidate best positioned to eat into the white working-class vote, which helped Trump win those three critical Midwestern/Rust Belt states. Among whites generally, Trump does 11 points worse against Biden than he did against Clinton four years ago.

Many of the recent polls used different age divisions, making it tricky to average group poll data and then compare it to the 2016 exit polls. But voters over 65 were included in most of the recent polls. In two, Trump is losing to Biden with those voters; in the third, he’s tied. That’s a big shift from 2016, when he beat Clinton by seven points with the oldest voting group.

Coronavirus has complicated traditional campaign efforts for President Trump and former vice president Joe Biden. (The Washington Post)

As I’ve already written 400 times in the past year, and as I will write 4,000 times between now and November: Things change. Trump wasn’t expected to win those three states in 2016, but: Things changed. These polls will shift in one way or another.

If you are Trump’s campaign, though, the numbers above are exactly why you didn’t want to see Biden on the other side of the November ballot.