The SHA-256 ( nonce + input string) = SHA-256(1Make America Great Again) does not start with zero. So we increment the nonce by 1. Finally on the 20th attempt we find the hash value such that it starts with zero. The SHA-256 input is ‘20Make America Great Again’. The number of zeroes that the output has to start with is known as the ‘Difficulty’. Now the goal is readjusted such that it is to find hash starting with 2 leading zeros.