Biblical basis or rationale for Christian Identity Movement? After discovering the Christian Identity movement, and investigating them further to answer another question, I've been pondering how they justify their doctrine.

On the homepage of Christian Identity Ministries they quote Luke 1:68-75 and then make this bold statement: 

"The Anglo-Saxon-Keltic-Germanic-Scandinavian People are Israel"

How does Christian Identity interpret the bible to justify a white supremacist theology?
In Luke here there's a prophecy about the restoration of Israel, pretty similar to many found in the psalms.
Some white supremacists, including these people, believe that the 10 lost tribes of Israel (all except Judah and Benjamin, I think) went to Northern Europe and became the English, and sometimes all the Celtic &amp; Germanic people.
So these verses about Israel being "saved" is evidence to their minds that all the tribes would be preserved, and they see their race as fulfilling that.

Read more about the ten lost tribes if you want to know more. 

This is a very biased belief that has almost zero historical evidence, and St. Paul has the view that Christians are the fulfilled children of Abraham (see his To The Romans).