20. Nxe2 would have been check. So you say white follows with 21. Nxe2, then black follows with 22. Bd3, then what White can't 23: Re2 because black can capture 24. Qxe2. If 24. queen on to light-square then Black can torment with Rook and Knight until the battle at xe2 is won.
20.Nd4 Nxe2
21.Nxe2 Bd3 (??)
22.b4 Qd8 (because Nxb4 would be loss of N and Qa4 would be met with Nec3 trapping the black queen in left flank)
23.Nd4 Re5 (best line of defence since Nxd4 would be met with Qxd4+ and subsequently Qxd3 taking the black bishop and an all out attack possible from move 24 hece the bad move notation ??)
If we had to get to Re5 as a defence it is far better to do it at move 20 (instead of Nxe2 and giving away a solid position). If you really have to do 20. Nd4 Nxe2, there are other defences possible after 21. Nxe2 but Bd3 is not it, in fact it simply gives the game to white in 4-5 moves.
Move 24 has ramifications in this theoretical position we are discussing, so I will not bring it up. Anyways we should probably play to the position now in interest of not derailing it.