Pete Buttigieg wins Iowa, but no Democrat arrives at the convention with a majority. The nomination requires delegates switching sides after the initial first vote or a second ballot where superdelegates are permitted to participate. I pick Mr. Biden to win, but I’d take the field if I could.

Because Democrats are concentrated in California and New York, Mr. Trump trails in the popular vote. Mr. Trump wins Florida. Ohio, now redder, isn’t in play. Iowa swings Democratic. Mr. Trump does better than in 2016 among African-American and Latino voters.

The election again comes down to Michigan, Pennsylvania and Wisconsin. Mr. Trump must win at least two. They’re settled by a wider margin than the 77,744 votes of the 13,940,912 these Blue Wall states cast in 2016. Victory depends on Mr. Trump’s discipline and whom the Democrats nominate. If it’s Mr. Biden, Mr. Trump has an uphill fight; if not, the president wins.

Republicans keep the Senate and Democrats the House, both with smaller majorities.