Chuck Schumer, the senior Democratic senator from New York, already has one of his talking points for 2012 — he plans to lambaste the Republicans for their “tax cuts for millionaires,” a reference to the right’s refusal to end the Bush tax breaks at the upper-end of the income distribution.

That’s a big deal, because for much of the post-war era, class has been a forbidden subject in U.S. politics. Americans were sold on the idea of living in the land of opportunity — their country, after all, was the one huddled masses fled to for the chance to build a better life. That self-image was so appealing and so powerful that politicians ran against it at their peril—Morning in America played better on the campaign trail than class war.

Schumer is a centrist whose constituency includes many of America’s plutocrats —he has sometimes been called the Senator from Wall Street. He is also one of the country’s savviest politicians. So his judgment that “millionaires tax break” will make a good bludgeon for Republicans says a lot about how deep the chasm has become between America’s super-elite and everyone else, and how worried middle-class Americans are that the old promise of social mobility is no longer delivering.

Liberals concerned about this divide have focused on the ways in which it has been created by pro-rich tax policies, a concern documented in Winner-Take-All Politics by Jacob Hacker and Paul Pierson, and further stoked by this week’s tax deal. That’s a legitimate gripe.

But the two Americas are moving further and further apart for another reason, too, and it is one over which U.S. legislators and U.S. voters have little control. After a century when succeeding in America was the surest route to commercial success, the country’s best businessmen and women have realized that the way to win is to go global.