Scott Walker was talking about this back in April - 3 months before he announced his presidential run in mid-July.
Walker is being forced to come out of the closet on the immigration issue. I doubt he will be as forthright and bold as Trump who has put out the most detailed plan about immigration. Santorum is the only one to have done something similar. So where is the Walker position paper on immigration? Give me a link.
Sessions has leading on immigration and amnesty issues since at least 2006. Walker was for amnesty only a few months ago.