Show them hospitality.
Give them justice.
Hold them accountable.
I believe that these are the answers one can come to by reflecting on the Law of Moses and the life of Christ.
When Christians living in a representative democracy go to vote on laws regarding immigration, I think they need to ask the following questions before giving or withholding their support:
Does this legislation exhibit hospitality to immigrants?
Does this legislation deal justly with immigrants?
Does this legislation hold immigrants accountable before the laws of the state/country?
Christians may not all vote the same way, but we should all share the same standards for deciding how we should vote.