In one universe, Kamala Harris leads only narrowly in the national popular vote against Donald J. Trump, even as she holds a discernible edge in the Northern battlegrounds. The numbers look surprisingly similar to the 2022 midterm election.

In the other, Ms. Harris has a clear lead in the national vote, but the battlegrounds are very tight. It’s essentially a repeat of the 2020 election.

This divide is almost entirely explained by whether a pollster uses “weighting on recalled vote,” which means trying to account for how voters say they voted in the last election.