A true horse race

This month is offering a serial look at the strengths and weaknesses of our candidates for president. Iowa provided insight into their ground games: Barack Obama stirred the young and the loyal, while Hillary Rodham Clinton fizzled; Mike Huckabee energized the Christian right, where support for Mitt Romney failed to gel. Then New Hampshire brought out the mainstays of the parties: Older women warmed to Clinton and propelled her to a comeback; John McCain tapped old loyalists.

Now, in between those opening rounds and Super-Duper Tuesday, those candidates face two more telling tests. Nevada gives the first look by Western voters and also a measure of union strength; South Carolina puts candidates before the first electorate with a significant black population. It is no stretch to imagine that at the end of these four races, the relative electability of the leading candidates will be clear for all to see -- and just in time for voters across the nation to cast the primary season’s definitive ballots.

Many pundits suggest that, on the Democratic side, it is Clinton who is best positioned. She enjoys strong support among labor unions, which ought to help her in Nevada, and she and her husband have long run well among African Americans, which ought to help in South Carolina. But both those assumptions seem vulnerable to Obama’s new momentum. The Culinary Workers union, said to be one of Nevada’s most significant, voted last week to endorse him. As for black voters, who could make up nearly half of South Carolina’s Democratic electorate, their historic support for the Clintons has never been put to a test quite like this.

If John Edwards cannot win Nevada or South Carolina -- one where he’s polled well, the other his home state -- his withdrawal would become all but inevitable and would raise the question of where his supporters will land when they scatter. Will they affiliate their economic populism with Clinton’s labor sympathies, or will they be drawn to Obama’s call for a new political discourse? The answer there could decide the Democratic nominee.

On the Republican side, the two contests will determine whether Rudolph W. Giuliani guessed correctly that he could skip the early states and jump in for the big ones in time to rescue his party from indecision. His strategy has been vindicated by the electorate so far, which has split along increasingly sharp fault lines -- there is no sign of any rapprochement between economic and social conservatives, no hint that Huckabee’s backers and McCain’s supporters see much in the way of common purpose. The only problem for Giuliani is that he’s dropped like a stone in national polls.

This quick succession of primaries is what has given American politics its singular excitement in 2008. It is all the more thrilling for what it will offer up Feb. 5: the chance to select two candidates to debate the nation’s future at this vital moment.