Djokovic has a mental edge over Federer and Rafa (except for on clay, where Rafa has won their last 3 meetings).
Anyway, it makes no difference, because Djokovic is well behind them in the slam race, and Rafa has a 2-1 record vs. Djokovic at the US Open.
Djokovic has never had a winning record over Rafa at the US Open, despite regularly having the 'mental edge'.
So what can Djokovic do in 2020? Not much, because Rafa has the edge at Roland Garros and US Open.
Djokovic wants nothing to do with Rafa in the Final, because it will mean Rafa has wrapped up the year-end-#1.
And Rafa can make sure they only meet in the Final, because Rafa plays on the last day of Round Robin and can choose his SF opponent
I doubt Djokovic is good enough to beat Medvedev in a SF anyway, so the Final will probably be Rafa vs. Medvedev.....or Federer vs. Medvedev.
Thiem is good enough to qualify for the SF too.