How can we say no? The people who might lose out from the Gang of Eight are harder to identify—though not impossible, which is why the immigration bill could yet be defeated. Many of the people who would lose out if same-sex marriage contributes to the decline of the institution aren’t even born yet.

Like the welfare state, the benefits are concentrated and the costs diffuse.

Even if every negative consequence predicted by the opponents of both innovations comes to pass, they can always be blamed on dozens of other factors. The people who vote yes will be seen as the winners of history, civil-rights heroes, no matter what.

For Republicans, often criticized for being the “party of no,” the political difficulties are obvious. They are often in the position of saying no, until eventually they are worn down, almost beaten into submission.

On both immigration and gay marriage, the party’s base is largely on one side and the new voters Republicans need to appeal to are on the other. The arguments that they will benefit politically from passing the immigration bill are weak. The case that they will be harmed by defeating it is somewhat stronger.