While Harriet Tubman might be a good replacement for the $20 bill, one could also consider other People of Color, such as Frederick Douglas and, perhaps even more appropriate, Indigenous people such as Sitting Bull or Chief Joseph, both important leaders of the Indian resistance to the European colonists.
Moving away from political correctness, one might also consider FDR who successfully led the country through the ordeal of the Second World War.
Lastly, there is poor old, grouchy John Adams who got a bad deal, since he was our second president, but for some unknown reason, got left out of the currency picture contest.
Leonard Cohen
Northampton