If it is Trump v Biden part deux in 2024 the electoral college race will come down to a total of 4 swing states.... Arizona, Georgia, Pennsylvania and Wisconsin

That is according to the' Cook Political Report'

A Very Narrow Electoral College Playing Field | Cook Political Report

University of Virginia’s Center for Politics has come to the same conclusion.
Four swing states that will determine the 2024 presidential election (yahoo.com)

The problem for both parties is that to win the nomination their candidate must own the base . But the base is not enough to win the general election. Polarizing politics has reduced what was once a number of states down to the 4 . The last 2 elections there were 6 . I am not sure that the other 2 aren't in play. North Carolina was a swing state but it will most likely go blue. Michigan was a swing state that will likely go blue . Florida was a swing state that is now solid red.

2016 Michigan Pennsylvania Wisconsin were swing states that Trump won . 2020 he lost them all.