Waterloo, Iowa — The most important development today – by far – was Barack Obama’s decision to take out after John Edwards on health care (even more important than the just announced Des Moines Register endorsement of Hillary Clinton).

“Senator Edwards, he and I have similar plans,” Obama said during a town-hall in Independence , Iowa. “I think he’s done some good work . But he argued, that, you know, ‘Barack, he thinks you can negotiate with insurance companies and drug companies and drug companies. And I think you’ve got to just beat ‘em. ‘ You know what? The key to getting this done is to empower the American people, but you also have to have negotiations and you to be able to listen. Otherwise stuff is not going to happen. So we want to reduce the power of drug companies, insurance companies and so forth, but the notion that they will have no say at all in anything — that’s just not realistic. It’s not true.”

Hours later in Dubuque, Edwards called Obama’s take “fantasy” and that achieving universal health care coverage would take a fight and a fighter willing to make the fight. “We have a different approach and I think voters should know what the differences are,” Edwards said. “There is no way the president of the United States should be negotiating with drug companies and my responsibility as president should be to fight on behalf of America.”

Why does this matter?

Because if the axis in the Iowa race turns less and less on the Obama-Clinton dynamic and more on Obama versus Edwards on policy and politics, the race in Iowa will change dramatically.

Understandably, camp Edwards has chafed at watching as Hillary and Barack have sucked up most of the media space (though not mine, I’ve never counted Edwards out here and have said so over and over…check the transcripts).But now they sense Clinton could be in real trouble and are poised to tell Democrats the time to fight is now.

Based on the reaction in the Fox focus group after the Thursday Iowa Public Television debate, Edwards has reason to hope for (and quite possibly expect) the best.

In their conference call today, deputy campaign manager Jonathan Prince and senior adviser Joe Trippi virtually bristled with confidence, calling Iowa a statistical tie but classifying Edwards as the candidate with new-found momentum (I know, what else would you expect them to say?).Many of us have been on these calls and this one conveyed a need degree of confidence. Before today, Edwards chieftains often spoke abstractly of expectations that “X, Y, and Z will happen.” Today they cited fund-raising, web-traffic and volunteer sign-up activity that bespoke newfound excitement and energy as all three campaigns move into what is universally regarded as the last week when you can really harness new supporters before the crush of post-New Year’s undecideds start making up their minds.

For Democrats in Iowa and the rest of the country, if a debate between Edwards and Obama breaks out on policy and politics, its resolution will have deeper consequences than the current Clinton-Obama debate.

Why?

Because the Clinton-Obama debate is at one level about old versus new in the traditional confines of a long-running Democratic debate about governance. Obama supporters, generally, want many of the same policy positions Hillary espouses, but they want them pursued with an energy and conviction that they believe in, not just because the Clinton “machine” tells them to believe in it or creates a “war room” architecture to achieve it.

The essence of the difference, generally, is Obama supporters want to feel and keep feeling the enjoyment of riding the Obama wave and tell themselves big dreams and big history are possible.Writ large, the Obama and Clinton race has been one of “big dreams” versus “big seriousness,” or “big excitement” versus “big experience,” or “big crowds” versus “big endorsements,” or “big hopes” versus “big inevitability.”

If in Iowa, that choice morphs into an Obama-Edwards conflict, what’s the short-hand? There can be no other: “Big dreamer” versus “Big fighter.” If Iowa Democrats pick the “Big fighter” over the “Big Dreamer” and Clinton comes in third (by no means certain, but definitely possible), then Clinton will have a two-way fight ahead of her in New Hampshire because she can’t afford to ignore either.

Obama, having “lost” in Iowa will have to confront the possible limitations of the politics of hope. And Edwards will have to try to find a way to get undeclared voters in New Hampshire as angry about “corporate greed” as Iowa Democrats were.If he does, the long-dormant “fighter” gene in liberal/progressive/populist politics may come back to life and that could change the face of the race and, possibly, the presidency (as camp Edwards loves to say — populism is driving who in the GOP side? Mike Huckabee. No accident, say the Edwardians).

Today stood out because Obama and Edwards have basically ignored one another the last two months. Reporters have tried tirelessly to provoke Edwards to knock Obama and he’s demurred. Obama has just flat ignored Edwards, training his sights on Hillary and hoping/calculating that Hillary’s Billy Shaheen agony would distract from Edwards’s widely praised debate performance.

What accounts for Obama bringing up Edwards today?

The only answer can be a sense in the Obama camp that Edwards now presents as big, if not bigger, Iowa challenge than Hillary.Team Edwards also believes this to be true. Clinton’s camp is trying to prop Hillary up here with the five-day Hil-A-Copter tour (Obama cracked today he’ll get around on “a magic carpet”).

If Edwards and Obama begin to engage each other more directly in the coming days, you will know that both see Hillary’s numbers declining and her organization coming apart. And that will signal a brand new phase of this race with unpredictable consequences for all involved.