Maybe Jack Lew has never heard the Johnny Horton song about the battle of New Orleans ("In 1814 we took a little trip, along with Col. Jackson down the mighty Mississipp'"). If the British had won that battle they might have torn up the Treaty of Ghent and demanded the US give up some of its western lands if we wanted to end the war. (That was before Napoleon escaped from Elba.)
Tubman is a deserving figure and better than the other names that had been thrown out there but I would have preferred a different denomination be the one chosen.