There have been only two instances of presidential second rounds with the extreme right: J.Chirac vs. JM.Le Pen in 2002 (Chirac won with 80%) and E.Macron vs. Marine Le Pen in 2017 (Macron won with 67%).

In each case, many left voters cast their ballot holding their nose, but with a clear aim to prevent a Le Pen from getting to the Élysée. Hence, the outsized scores, much higher than "regular" left-right presidential races.

Macron is obviously betting that, like in 2017, the left voters detestation of the extreme right will surpass their detestation of Macron's LREM. This is a risky gambit and many things may happen in the next two years.