Quick, what is the second largest terrorist attack in the USA? Or the third, fourth or fifth?

Respectively they were the Oklahoma City bombing, a white riot killing blacks in Tulsa, a massacre by Mormons (!), and a white riot killing blacks in Louisiana. https://en.wikipedia.org/wiki/Terrorism_in_the_United_States#Deadliest_attacks

Quick, how many Americans have been killed in terrorist attacks by citizens of the six nations affected by this travel ban?

Zero. 

Physician, heal yourself.