It is not a challenge to the US.
If I go to Mexico with a .22 round in my pants pocket or in my car I have violated Mexican law and can be sentenced to a lengthy prison stay there. And it's happened many times over the last few years. A guy from a Texas border town will go across the border with a box of rifle ammo and they'll search his car. They will arrest me and they will send me to prison unless my family can pay the bribe quick enough to keep me out of the system.
Afghanistan's laws say it is ok to perform charity in their country as a Christian, but they do not allow you to attempt to convert people from Islam to Christianity or any other religion. These missionaries knew it and knowingly broke the law. I feel bad for them, but they knew there would be a consequence if they did it. As people of faith, I'm sure they expect the Lord to see them through on this, and he just may. Or, they may become martyrs. They certainly won't be the first or last Christian martyrs.
God Bless Texas