Turn it around on them.
Immigration advocates like to take advantage of White Christian guilt, asserting that Jesus would want White Americans to sacrifice their own interests in order to help all the needy immigrants who desire a better life for themselves. "What would Jesus do?" "Who would Jesus deport?" We've all heard that.
I myself am not Christian and am instead more of a national socialist Nietzschean atheist. But I do have some advice for White Christian racialists who encounter such arguments (and this applies anywhere, not just for America).
The "Jesus-Christian-sacrifice for others" meme can be turned around. After all, if Jesus says that White Americans need to sacrifice their interests to help foreigners, immigrants, etc., then the opposite is true - Jesus would like all those foreigners and immigrants to sacrifice their own interests to help poor Americans.
Now, then - think of all those Americans harmed by immigration. Think about blue collar workers outcompeted by low-skilled immigrants, people losing jobs to (cheap labor) immigrants, people losing out to immigration (and outsourcing). Think about white collar workers being outcompeted by (cheap labor and ethnically nepotistic) high-skilled immigrants. Think of Americans and their posterity being displaced, being crowded out, by immigrants.Think of all those poor Americans - all those American children - losing out, losing opportunities, losing their nation, losing everything, because of immigration. Think of all those fatcats making money off of cheap immigrant labor while Americans go without. What would Jesus do? Indeed! Obviously, these foreigners and these immigrants - those that consider themselves good Christians - should sacrifice their own selfish interests and help poor suffering Americans. In order to help these Americans, these foreigners should stay in their own countries, rather than come to America and take bread out of the mouths of Americans, from all the needy American children. Who would Jesus displace? No one! Stop being selfish and taking the lands of others! Stay home and care for yourselves, all you Christian foreigners, and help needy Americans get back on their feet!
That's Jesus' double edged sword. Sacrifice for others applies to foreigners and immigrants just as it does for White Americans. Do unto others applies to foreigners and immigrants as well - if they wouldn't want their own nations stolen from them, don't to it to others.
That's the Christian thing to do, no?