At first glance, becoming president looks like simple arithmetic: Carry at least 90% of your party’s adherents and win more independents than the other candidate and voilà, you’re in the White House.
That’s how Donald Trump won in 2016. He took 90% of Republicans and 48% of independents, while Hillary Clinton won 42% of independents. It’s also how Joe Biden defeated Mr. Trump four years later. He received 94% of Democrats and 54% of independents. The equation works as long as there is near-parity between the parties, as in 2020 when the electorate was 36% Republican, 37% Democratic and 26% independent.
Still, given how close the last two presidential races were, small changes in partisanship in key states can have huge consequences. A mere 77,744 total votes in Michigan, Pennsylvania and Wisconsin gave Mr. Trump his victory in 2016, and 42,918 votes in Arizona, Georgia and Wisconsin produced Mr. Biden’s 2020 victory.
The political makeup of several swing states has changed in the past four years. Having voted Democratic for president since 2008, Nevada is more of a battleground this cycle because of a declining Democratic registration advantage. Nevada has 32,856 more registered Democrats than Republicans, a decline of 53,867 since November 2020. Mr. Biden won the state by 33,596 votes. The Democratic registration advantage over Republicans in Pennsylvania is 399,494, a decline of 286,324. Mr. Biden carried the Keystone State by 81,166.
While those states swung right, Arizona and North Carolina have possibly done the opposite. In the Grand Canyon State, independents grew from 31.8% of registrations in November 2020 to 34.1% today. Republican voter registrations were nearly flat while the Democratic share dropped about 3 points, to 29.3%. In the Tar Heel State, “unaffiliated” voters grew from 33.3% of the rolls in November 2020 to 36.8% as of March 30. Republicans dipped a little, going from 30.3% of all voters to 30%, while Democrats dropped from 35.6% to 32.3% of voters. But new independent voters in both states appeared to be mostly the college-educated suburbanites who disfavored Mr. Trump in 2020.
Three battleground states—Georgia, Michigan and Wisconsin—don’t register voters by party, so trends in those states are harder to discern. But there is enough movement in the other four swing states to give both the Biden and Trump camps indigestion. And that’s before taking account of turnout.
The Biden high command is worried about turnout among black, Hispanic and young voters. It should be. These groups could sink the president if they aren’t revved up for him and his party.
In Arizona, Hispanic voters accounted for 19% of the 2020 electorate and broke for Mr. Biden 61% to 37%. Voters under 30 made up 16% of the electorate and went for him 63% to 32%. A decline of roughly half a percentage point in either group’s share of the electorate could be enough to flip the state red. Similarly, blacks accounted for 29% of Georgia’s electorate in 2020. They broke 88% to 11% for Mr. Biden. A decline of 0.3 percentage point in the black share of the electorate wipes out Mr. Biden’s victory, all else being equal.
A lack of enthusiasm among Democrats is probably why Mr. Biden trails Mr. Trump in six of seven battlegrounds in a new poll from The Wall Street Journal. Mr. Trump falls short of 50% in all of them. While the president flails, his predecessor hasn’t closed the sale.
