If Obama's proposal demonstrates genuine neutrality between public and private health options -- empowering individuals to make a free choice -- it could gain significant Republican support. If the plan is an intermediary step toward a single-payer system, Obama can expect a serious fight, even from a weakened opponent, because the deepest values of American conservatism will be at stake.

Second, the scale of Obama's environmental ambitions has been highlighted by the current economic crisis.

It is another iron rule that prosperous, confident nations do more for the environment than economically struggling ones. And this sets up a conflict between Obama's urgent environmental diagnosis -- a cumulative scientific case for serious, possibly catastrophic climate disruption -- and the economic and political realities of the moment.

The centerpiece of Obama's environmental approach is an "economy-wide cap-and-trade program," designed to dramatically limit greenhouse gas production. But this would act as a large tax on the use of fossil fuels -- in an economy where falling energy prices have been one of the few sources of good news.

If Obama plows ahead with an aggressive cap-and-trade system, Republican and Democratic opponents -- focused exclusively on jobs -- will find plenty of excuses for legislative inertia. If he phases in a system too slowly, it will undermine his own arguments for urgency. If he abandons a cap-and-trade system in favor of investing in eco-infrastructure -- a more efficient energy grid, weatherizing public buildings -- he will get what he wants, and also get slammed for betraying a serious commitment.

During the campaign, I sometimes criticized Obama for lacking specificity and ambition. But as the specifics emerge, the ambitions of his campaign pledges are ever more clear.