The immigration debate is moving into high gear as the Senate Gang of Eight release their bipartisan reform plan this week. We'll take some time to study the details. But for today let's step back and consider the central question that's been debated since the great wave of Ellis Island immigrants a century ago: Do foreign newcomers contribute more to the economy than they cost?

Republican Senator Jeff Sessions of Alabama, a reform opponent, contends that the net cost of the Senate plan "would be enormous," reaching...