Conservatism's long heyday in national politics is grinding to an ugly halt.

The demise may have been inevitable; cue in Eric Hoffer's oft-quoted line that every cause begins as a movement, turns into a business and degenerates into a racket.

But the conservative movement managed to set the terms of national discourse for nearly three decades because it did some things very well.

Chief among them, it cultivated greenhouses for ideas: think tanks such as the American Enterprise Institute, flagship journals such as the National Review.

There, theories, policies and political narratives flowered in profusion. Politicians needed only to snip the blossoms and display them on their lapels.

Liberalism, by contrast, had a thinner intellectual bench. What it had in profusion were interest groups with laundry lists of demands.

Recently, responding to its skein of deplorable defeats, the left half of the spectrum has emulated the right in creating think tanks such as the Center for American Progress and journals such as the American Prospect.

Exasperated critics of Barack Obama frequently complain that his relentless calls for "change you can believe in" are short on content. His speeches are vague (though his Web site offers plenty of specifics).

One way to guess what Obama might do is to look at what ideas are brewing along his ideological supply chain of thinkers and writers. A good place to start looking is the spring issue of Democracy: A Journal of Ideas. There, 20 smart writers offer up their best "big ideas" for a new, progressive agenda.

Here are five that struck me as particularly interesting:

1. A "third-age" initiative. This idea from Gara LaMarche of Atlantic Philanthropies responds to a rising realization. Retirement at 65 in a society where most people who reach that age will live 20 more years is just stupid. Boomers won't want to settle for the golf cart and the crosswords. But they will flee the Dilbert cubicles. They'll seek work of social meaning, in schools, hospitals and nonprofits. LaMarche suggests a tuition-assistance program to help seniors train for these "third-age" careers, perhaps using community colleges as a focal point.

2. A progressive consumption tax. This one is wild, but it gets you thinking. Robert Frank, an economics professor at Cornell University, has written brilliantly about upper-middle-class discontent inside America's culture of spiraling consumption. His idea: tax consumption, not income. Reward savings, to boost a puny national savings rate that is putting us scarily in hock to China. How? His idea is nearly as simple but a lot more progressive than that right-wing sacred cow, the flat tax. All you'd report to the IRS is how much you earned the previous year, minus how much you saved. The more you save, the less your taxable consumption. Most middle-income Americans would pay less. Corporate moguls who throw million-dollar birthday parties would pay a lot more.

3. Medicare for long-term care. One of the dirty little secrets of America's middle class is how it relies on Medicaid, supposedly an insurer of the poor, to pay for grandma's nursing-home care. This clumsy method invites abuse and will become unsustainable as the baby boomers age. Jeanne Lambrew, a fellow at the Center for American Progress, has a better idea. Use Medicare as the reinsurance backstop for long-term-care insurance plans that the feds would vet and monitor. This would make the insurance more affordable, understandable and attractive.

4. Pay-as-you-drive car insurance. This idea from Jason Bordoff of the Brookings Institution is startlingly simple. The more you drive your car, the more you'd be charged for insurance. This would pool risk as effectively as insurers' current Byzantine rating systems. In an era of an oil crunch and global warming, it would be a powerful incentive to curb the number of miles you drive.

5. Middle-class schools for all. How can we get children from low-income households to learn? Liberalism's past big ideas, from busing to blitzing high-poverty schools with resources, haven't worked. Neither have school vouchers, the right's ruling obsession. Richard Kahlenberg, a fellow at the Century Foundation, notes that one of the top predictors of academic failure is attending a high-poverty school. So why not make economically integrated schools your core goal? Wake County, N.C., is trying this, and it seems to be working.

Other "big ideas" in this package deal with items such as gun crime, diplomacy in the Muslim world, smart growth and government reform. It's worth your time to check it out www.democracyjournal.org

Center Square also appears Saturdays in the Local News section. To comment, call 215-854-4243 or e-mail csatullo@phillynews.com.