U.S. Rep. Dennis Kucinich, D-Ohio, speaks at Western State Hospital in Lakewood, Wash., in 2011. Kucinich announced this week that he would leave Congress after eight terms. (Ted S. Warren/AP)

It is the Hope Diamond of liberal ideas: pure, breathtaking and highly impractical in the real world.

The proposal has been submitted for consideration in every Congress since 2001, and the idea behind it is that the federal government could stop wars, pacify street gangs, and distill violence out of the American soul itself. All it would take was a new Cabinet-level department and $10 billion a year in taxpayer money.

But now the ultimate Capitol Hill long shot — the “U.S. Department of Peace” — is looking even less likely than usual. It is losing its champion in the House.

“Of course it could work,” said Rep. Dennis Kucinich (D-Ohio) in an interview last week. “It’s very practical. You know, I’m a practical politician.”

Last week, Kucinich announced that he would leave Congress after eight terms.

Earlier this year, he had lost a primary contest against Rep. Marcy Kaptur (D), whose district had been merged with Kucinich’s. Then Kucinich gave up on his backup plan: moving to Washington state and running for a new seat there.

Kucinich’s departure will remove one of the most colorful characters from Congress’s daily melodrama: an antiwar vegan ventriloquist who once saw a UFO while hanging out with Shirley MacLaine.

But it will also take a little vim out of the Capitol’s battle of ideas, by removing a legislator who was unafraid to put 200-proof liberalism down on paper. During his time in Congress, Kucinich sponsored bills to create universal pre-kindergarten, to eliminate the federal death penalty and nuclear weapons, and to impeach both President George W. Bush and Vice President Dick Cheney.

His ideas were rarely more audacious — or more complicated — than HR 808, a proposal to defeat violence, at home and abroad, through the liberal application of government. This was Kucinich’s formulation of an idea that had been around, at least rhetorically, since the days of the Founding Fathers.

Now, at Kucinich’s political passing, we pause to remember it.

“How can we construct more peaceful selves, homes, cities, nations and the world?” Kucinich said this week, describing the bill’s goal. “The Department of Peace was not just some airy-fairy notion of, ‘Let’s all get together and sing “Kumbaya.” ’ Which is okay with me. But the Department of Peace is a highly structured approach that puts a permanent place for peace in our national discussion.”

Here’s how the bill would work:

A secretary of peace would sit in the president’s Cabinet and on the National Security Council. The secretary would be given a special new role in the country’s military decisions: If a conflict was about to start, the secretaries of defense and state would have to consult the Peace secretary “concerning nonviolent means of conflict resolution.”

But the new department would be concerned with much more than foreign wars.

It would also seek to stop bloodshed in U.S. cities, by funding stop-the-violence programs, programs in schools and “unarmed civilian peacekeeping.”

There would also be a Peace Academy, modeled after the military service academies. After four years, graduates would be required to spend five years in public service, promoting conflict resolution at home or abroad.

And the bill would encourage the establishment of a Peace Day. “Such day shall include discussions of the professional activities and achievements in the lives of peacemakers,” the bill says.

The cost of all this? The bill asks for $10 billion per year. That’s a little more than the Environmental Protection Agency and a little less than the Department of Commerce.

In the current Congress, focused so heavily on spending and debt, this sounds less like legislation and more like an attempt to give a tea party Republican a stroke.

But Kucinich’s argument is that — if it worked — the Department of Peace would save money in the end.

“I think that my position is actually a conservative position. Peace is becoming the conservative position,” Kucinich said. By not getting into military conflicts, he said, “we conserve lives. We conserve America’s resources. We conserve America’s money.”

He never got the chance: The bill has been introduced now six times, and never made it out of committee. But Kucinich believes that the bill will carry on when he’s gone: He has been looking for a colleague to take it up next year.

Maybe even a Republican.

“It’ll get reintroduced. No question about it,” Kucinich said. “This is an idea whose time is coming.”