The immigration proposal pending in Congress would transform the nation’s political landscape for a generation or more — pumping as many as 11 million new Hispanic voters into the electorate a decade from now in ways that, if current trends hold, would produce an electoral bonanza for Democrats and cripple Republican prospects in many states they now win easily.

Beneath the philosophical debates about amnesty and border security, there are brass-tacks partisan calculations driving the thinking of lawmakers in both parties over comprehensive immigration reform, which in its current form offers a pathway to citizenship — and full voting rights — for a group of undocumented residents that roughly equals the population of Ohio, the nation’s seventh-largest state.