The mathematics of the electoral college.

The 2020 Presidential election was one for the history books. President Biden won the office by winning back from Donald Trump certain swing or battleground states that Trump won in 2016. Explain the mathematics of the electoral college. Identify those key swing states. Why did Biden win them back from Trump? Many Trump supporters claim that Trump won those states again in 2020. What is their main argument? Again, https://www.realclearpolitics.com