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WASHINGTON -- The winnowing process in the Republican presidential nomination race has now reduced the field to four candidates -- Mitt Romney, Ron Paul, Rick Santorum and Newt Gingrich -- each of whom has a legitimate rationale to keep going.

Romney continues to have the most money and largest field organization. Santorum has recent, if modest, primary or caucus successes to sustain him. Gingrich has his immense ego and a rabid following to drive him on. And Paul has his own goal of advancing a libertarian strain in the Republican Party quite apart from achieving the nomination, and an idealistic and undaunted youth brigade behind him.

With Romney failing to gain clear majorities of voters in the preliminaries to date, and with no message that seems to promise a broader constituency, there's no reason for the other candidates to fold up. The free televised debates, though temporarily in suspension, will resume soon, enabling them remain visible to millions of voters.

Between now and the next primaries in Arizona and Michigan on Feb. 28, the Super-PACs supporting Romney and Gingrich can be expected to fire a host of negative advertising at Santorum. The latest New York Times/CBS News survey has him at 30 percent support to 27 for Romney, 12 for Paul and only 10 Gingrich.

The former House speaker has been fading so fast that ordinarily a candidate in his straits would be expected to drop out soon. But Gingrich has vowed to stay in the race into the convention, and a combination of more impressive debate performances and his immense self-assurance could well keep him going.

So what happens if this quartet of presidential wannabes hangs in, with none of them catching fire but each of them picking up a share of the national convention delegates as the process proceeds? With many states allocating them in proportion to the percentage of votes won in the primaries and caucuses, split decisions in many states seem entirely possible this year.

To clinch the Republican nomination this year, 1,144 delegates will be required and the nose count is only just beginning. According to the CBS News tally so far, Romney has 100 committed delegates to 44 for Santorum, 29 for Gingrich and 15 for Paul. Unless Romney does a much better job articulating his personal narrative and agenda, it's not inconceivable that the current mixed bag of results will continue.

Santorum, heady over his recent surge, already is talking of dealing Romney another setback in his native state of Michigan, where his father George was a very popular governor and where Mitt himself was raised. Such an outcome would be at least a psychological jolt to Romney's stalling campaign.

A dozen more Republican contests in early March, including a primary in his adopted Massachusetts and in the key swing state of Ohio, could clarify the picture, but they also could reinforce the muddled race. Most of the largest and delegate-rich states, including New York, Texas and Pennsylvania, will not hold their primaries until April, and California not until June, all incentives for the four surviving Republicans to endure through them.

After the last state contests are over, if no candidate has acquired the delegate majority for nomination, Republicans could see the first deal in a smoke-filled room since 1920, when from a field of nearly a dozen vote-getters the Republicans finally chose Sen. Warren G. Harding of Ohio on the tenth ballot.

That year, the brokered convention fired up the Republicans, and Harding was elected. But the same year the Democratic nominee, Gov. James M. Cox of Ohio, needed 38 ballots in a similar situation to be picked, and he lost.

This summer, there would be no any guarantee in a brokered convention that any of the candidates who have slogged through the process would be anointed. Some states might belatedly put forward favorite sons, further complicating the picture. Even the opportunistic Sarah Palin might jump in. Could some dark horse who hasn't competed in the primaries and caucuses be nominated? In this crazy Republican year, it seems anything is possible.

(Jules Witcover's latest book is Joe Biden: A Life of Trial and Redemption" (William Morrow). You can respond to this column at juleswitcover@comcast.net.)