A White House official said Wednesday Congress needs to limit "chain migration" as part of a deal to grant citizenship to young people living in the country illegally because not doing so could trigger the largest immigrant wave “in the history of the world.” The official, speaking on background with reporters, said if young people currently eligible for the Deferred Action for Childhood Arrivals program are allowed to sponsor more than spouses and children, you can take “whatever number they give you, and multiply it by three or four.” “Each two immigrants averages seven sponsorships. A legalization of 2 million...