Following the 2016 presidential election, there were 206 Pivot Counties that voted for Barack Obama (D) in 2008 and 2012 before voting for Donald Trump (R) in 2016.
Based on unofficial 2020 results, there were 22 Boomerang Pivot Counties, which flipped to Joe Biden (D), and 174 Retained Pivot Counties, which voted for Trump again.
In 2016, Trump’s average margin of victory in what are now the 22 Boomerang Pivot Counties counties was 1.97 percentage points, 9.45 points fewer than his average across all Pivot Counties. By contrast, Obama overperformed in these counties, relative to his overall averages, in 2012 and 2008.
On the other hand, compared to 2016, Trump’s average margin of victory in the 174 Retained Pivot Counties increased by 2.15 percentage points. Trump had overperformed in the Retained Pivot Counties in 2016, exceeding his overall average margin of victory by 1.06 percentage points. Obama underperformed in these counties in 2008 and 2012.
To learn more about Boomerang Pivot Counties, click here: https://ballotpedia.org/Election_results,_2020:_Boomerang_Pivot_Counties
To learn more about Retained Pivot Counties, click here: https://ballotpedia.org/Election_results,_2020:_Retained_Pivot_Counties