Migration between Mexico and the United States is getting a lot of scrutiny under President Donald Trump. But the fact is, people have been crossing the US-Mexico border from the moment it came into being. Historian Ana Raquel Minian speaks with The World's Monica Campbell about that long history of migration between the two nations, and what that means in the context of Trump's immigration crackdown. Minian has a new book out called, “Undocumented Lives