THE NOTE: Final Four:

Jan. 31, 2008 -- We'll be short one son of a mill worker in Los Angeles Thursday night. On Wednesday, the Republican candidates somehow went 90 entire minutes debating each other without anyone saying some variation of, "as I demonstrated on 9/11."

So we have our Final Four, the early-voting states finally clearing the field the way they were designed to do (and maybe helped by self-fulfilling mainstream media prophecies; lots of brackets filled out last March had these pairs as the last candidates standing). The matchups are set for Feb. 5 -- and while it's easier to make the delegate math work now, we're still a long way from knowing who our nominees are.

Thursday at 8 pm ET, we get the Big Dance, the showdown we've been waiting patiently for: Two Democratic candidates on a debate stage, both vying to make history, but only one, of course, destined to come out on top.

Sen. Hillary Rodham Clinton and Sen. Barack Obama come to this fight with their differing backgrounds and messages -- but their biggest challenge this week is a tactical one: managing a primary schedule that's designed to keep things interesting for a long while. On Thursday, they'll again seek to find differences where there often aren't any, with the race already having taken a turn to the personal.

"Clinton and Obama are in a frequently nasty personal fight, but not one that reflects deep ideological divisions or, as yet, threatens to leave the party badly divided once it is over," Dan Balz and Anne Kornblut write in The Washington Post. "Republicans on the other hand, see the prospect of a clear fracture in their coalition as a result of the nomination contest."

On stage on Thursday, there will be "no foils, no subtle alliances and no triangulation," the Chicago Tribune's Christi Parsons and Mike Dorning write.

So we can expect to hear about our friends Rezko and Wal-Mart (more on that below) -- and just perhaps about "two Americas," even without John Edwards on stage. With Edwards ending his fight, both candidates are making quick plays for his former supporters -- and maybe for Edwards himself.

"Mr. Edwards was not saying what he would do, but aides to Mr. Obama and Mrs. Clinton said they planned to push themes in the days ahead that were directed at supporters of Mr. Edwards, who are now in the market for a new candidate," Adam Nagourney and Jeff Zeleny write in The New York Times.

One of the many things that makes these races fun is that both parties' establishments are deeply split. Clinton, D-N.Y., and Obama, D-Ill., each have their own claims to different Democratic establishments; now, with all the principals on the trail, we'll see if the Kerry-Kennedy combo can match Bill Clinton in star power/news value/real impact.

Clinton and Obama enter this critical phase with different messages -- one more taste of the role reversals that have marked this chaotic political year. Obama traveled to Denver -- where he hopes to cap his journey to the nomination this summer -- to lay out the stakes as he sees them (and in his most explicitly Clinton-bashing way yet).

Read between these lines: "We can be a party that tries to beat the other side by practicing the same do-anything, say-anything, divisive politics that has stood in the way of progress, or we can be a party that puts an end to it," Obama said, per ABC's David Wright, Andy Fies, and Sunlen Miller.

"I know it is tempting -- after another presidency by a man named George Bush -- to simply turn back the clock, and to build a bridge back to the 20th century."

It was a quick pivot to the one-on-one that the campaign now is: "His barbs never mentioned his rival by name, but Obama took a direct slap at Clinton's past divisiveness and her failure to achieve healthcare reform as first lady or senator," Maria L. La Ganga and Peter Nicholas write in the Los Angeles Times.

Responded Clinton, in an AP interview: "That certainly sounds audacious, but not hopeful."

Clinton is talking substance (and even "hope" of her own), planning a "national town hall" and releasing a new ad that focuses on the economy and the housing crisis.

And -- just as importantly -- she's trying to reclaim her campaign: Asked whether she can control her husband, she responded: "Oh, of course. You know, there's only one president at a time," Clinton told ABC's Cynthia McFadden for a "Nightline" piece that aired Wednesday.

On her husband's recent comments: "I think if whatever he said -- which was certainly never intended to cause any kind of offense to anyone -- that is the furthest thing from him," Clinton told McFadden. "And yet if it did take offense, I take responsibility and I'm sorry about that because we have nothing but the best intentions and the most hope about what we can do for our country."

This is another way to put it: "This is my campaign, it is about my candidacy," Clinton said on Wednesday, per ABC's Kate Snow, Jennifer Parker, Sarah Amos, and Eloise Harper.

(And on the "snub" -- she's got the line down pat: "I reached out my hand in friendship and unity and I'm still reaching it out and I expect we'll shake hands at the debate in California. Was it intentional, McFadden wanted to know? "You'll have to ask him. I don't know. But the differences between us are nothing compared to the differences between us and the Republicans. That's what I want people to stay focused on.")

On the Republican side, the endorsements that Sen. John McCain is picking up -- former mayor Rudolph Giuliani, R-N.Y., on Wednesday, with Gov. Arnold Schwarzenegger, R-Calif., coming Thursday, at 12:30 pm ET -- are big-time names, though they hardly hail from the conservative pantheon. (They were featured at the 2004 convention precisely because they looked and sounded different than so many of the delegates they addressed.)

They are trying to end former governor Mitt Romney's challenge -- but even as the establishment stirs, the stop-McCain forces remain potent (if less energized), in a race with clear ideological splits.

"Democrats have two candidates of unusual talent and political dexterity. Their political bases are equally formidable, as is their ability to raise money," Adam Nagourney writes in the Times.