The presidential election now moves to a new phase. There are discernible tiers among the candidates. There are clear patterns of money flowing to the campaigns. There is an outline of the issues that will make a difference. There is the beginning of a narrative to it all. Before long, if the various states ever stop trying to leapfrog in front of each other, there may even be a schedule.

This is true in both parties, but the Democratic race has clarified more dramatically than the Republican. Among the Democrats – assuming, of course, that former Vice President Al Gore does not plunge into the race with his Nobel around his neck – the outlines of the race are visible to all.

One element is the challenges that the candidates in the top tier face. Let’s agree for a moment that while Sen. Hillary Rodham Clinton of New York is the front-runner, two candidates (Sen. Barack Obama of Illinois and former Sen. John Edwards of North Carolina) remain within striking distance and thus are plausible alternatives. Here are the obstacles they confront:

¢ The “never” factor. Despite her lead in the polls, in the money race, in the attention derby, a cloud remains over the Clinton campaign – the fear that among the general public there is a sizable slice of voters who will not, under any circumstances, vote for Mrs. Clinton for president, not now, not ever. The last time this phenomenon appeared was during the years when Sen. Edward M. Kennedy, the Massachusetts Democrat, contemplated presidential campaigns in the 1970s and 1980s.

A Zogby Poll recently asked a sample of voters whether there are any candidates for whom they would never vote. Put aside the fact that 49 percent would never vote for Rep. Dennis Kucinich of Ohio and that 47 percent would never vote for former Sen. Mike Gravel of Alaska. Tune into any debate and you’ll see why. The finding that stands out is that exactly 50 percent of Americans say they would never vote for Mrs. Clinton.

Now it doesn’t take 50 percent to win the election, as Mrs. Clinton’s husband can tell her. He won with 43 percent the first time he ran, in 1992, and with 49 percent the second time, in 1996. Heck, Abraham Lincoln won with only 40 percent in 1860 and he has stood up pretty well to the verdict of history. But that is not the point. It’s tough to go into an election where half of the electorate is beyond your reach. This is the biggest challenge Clinton faces. She’s got a big sales job in front of her.

¢ The anger factor. This has emerged in recent weeks, as it has become clear that Barack Obama, often regarded as the candidate with the most potential, is falling far short of reaching it. One of the explanations: He’s competing for the votes of Democrats who are angry, really angry, about politics and President Bush, and he is talking about hope instead of revenge and repudiation.

A candidate has to run as the candidate he is, not as the candidate the polls say he should be, which is why former Rep. Richard A. Gephardt, who was never the wild protectionist and proponent of abortion rights he tried to portray himself, never became president, and why George H. W. Bush, who really did think supply-side economics was voodoo, needed eight years of ideological cleansing to win his party’s nomination. (This is the time someone ought to whisper a word of warning in the ear of former Gov. Mitt Romney of Massachusetts, but he’s a Republican and thus exempt from this morning’s homily.)

But in truth there is a little anger in Mr. Obama – anger over not being recognized for being against the Iraq war when Mrs. Clinton was marginally in support of it or at least didn’t obstruct Bush’s prosecution of it, and anger over being trapped by the Clinton campaign for sins of logic and policy he should be promoting rather than apologizing for. Maybe that anger will come out. If it does, it ought to be spontaneous, not contrived, though maybe he ought to contrive to be spontaneous about it before it is too late.

¢ The loneliness-of-the-laggard factor. John Edwards has the purest liberal positions in a party that seems to be in the mood to express liberalism in its purest form, and yet he runs third (though substantially better in Iowa, where his campaign will either flourish or fold). He has union endorsements galore: service workers, transport workers, carpenters, steelworkers, miners. This endorsement strategy can backfire – ask Walter Mondale – and in some ways it underlines Edwards’ weaknesses rather than his strengths.

But a new threat is appearing just beyond the far horizon. Mr. Edwards hardly talks about his Senate days anymore, and his days as the Democratic Party’s vice presidential nominee have disappeared into the fog, but before long you will begin to hear a quiet chorus of Democratic activists complaining about Edwards’ comportment (and, ultimately, competence) as the running mate to Sen. John F. Kerry, the 2004 nominee.

They’ll say that Edwards was off-message and off the reservation, which is politico-speak for saying that he forgot that Sen. Kerry was the nominee, not Sen. Edwards, that he didn’t behave like a hand-picked vice presidential choice who owed something to the man who chose him, that he didn’t listen to headquarters, that he was content to be a lone ranger in a close presidential election that might have gone another way had the Democratic ticket coordinated its efforts with more efficiency and ease.

This may make Mr. Edwards feel more isolated than ever – and maybe more liberated. The isolated candidates lose and the liberated ones have a chance.