It's a particular peril of reporting on the 2008 presidential election campaign in this early phase that impossibly large conclusions are drawn at absurdly premature moments from supposedly significant events. This applies to just about everything about the election but especially to the horse race aspect of the contest by which the media is always transfixed. Even in the late stages of a campaign interpreting polling numbers can be a risky business; at this stage it borders on the certifiably insane.

For a couple of weeks now the favorite piece of early conventional wisdom is that John McCain's campaign for the Republican nomination is in serious trouble. Just a month after he was almost universally agreed to be the prohibitive frontrunner for the nomination, the Arizona senator's campaign is now, in the view of a surprisingly large number of pundits, badly hobbled.

Commenting on CNN this week on McCain's slumping poll ratings, James Carville — not, to be sure, a wholly disinterested observer — declared that in his view McCain's "heart is not in it" and said he thought he would be out of the race entirely by the time of the Iowa caucuses. Anybody familiar with the battleship of a campaign operation McCain continues to build in northern Virginia would be a little surprised by that observation, but Carville was only voicing a more extreme view of what most pundits are saying. Stuart Rothenburg, a more objective commentator by any measure, wrote in Roll Call this week that it no longer looked as though McCain was the clear frontrunner.

Of course the poll numbers — as unreliable as they may be — are the main reason for this change of opinion on McCain. From a 20 point lead over all comers a few months ago, McCain now supposedly trails Rudolph Giuliani by about the same margin.

But even if you reject these early poll ratings as pure, speculative fluff — which you probably should — you can't deny that there are real political challenges for the McCain campaign that threaten to derail it.

What has changed, in just a few months, is the set of political conditions on which optimism about the McCain candidacy was largely predicated. It's far too soon to declare, as Carville did, the beginning of the end, but it's worth considering what has changed to the senator's detriment in the last few months.

Three big factors have changed in ways that have hurt him: the state of the Republican field, the early phase of the Democratic race, and the politics of the Iraq war.

The media has tried to characterize McCain's political positioning inside the Republican primary as a lunge rightwards in the last few years (evidenced apparently by his appearance at Jerry Falwell's Liberty University and a perfectly reasonable refusal to translate his opposition to Bush tax cuts to support for post-Bush tax increases).

In reality his political positioning has always been more of a defensive posture towards the right. No-one really thought he was going to ride to the Republican nomination on the shoulders of cheering evangelical Christians and Wall Street Journal Editorial Page supply-siders. But they did think that his generally conservative record on issues such as abortion, guns and gay marriage, his strong support for the Iraq war, as well as an aggressive campaign to win over erstwhile opponents from the Bush campaign in 2000 would persuade enough conservatives he was at least tolerable.

What's more, just last year it was a fair expectation that McCain's principal primary opponent would be a conservative favorite such as former Sen. George Allen. That would put an obvious cap on the number of conservatives he could plausibly win over. The McCain appeal in those circumstances then would be a modified version of what it was in 2000 — that, without overtly running against the party as he did seven years ago , he could demonstrate that he alone would be able to win over skeptical voters to the GOP in a general election.

But instead of a clear traditional conservative emerging, the Republican race has so far been a three-way contest between untraditional candidates. McCain has not advanced much with a conservative base that still distrusts him and has found himself competing for broader popularity with two quite appealing alternatives. It is no longer clear, measured against Rudolph Giuliani and Mitt Romney, that McCain is the only Republican who can appeal to a broader electorate.

The second factor that has not gone McCain's way in the last few months is the Democratic primary.

The Arizona senator was always any Republican's best insurance policy against a Hillary Clinton presidency. As long as it seemed certain that Clinton would be the Democratic nominee, republicans of all sorts could swallow their doubts about him and choose him as the candidate most likely to defeat her.

But the Democrats are not cooperating. The emergence of Barack Obama changes the contours of a potential general election campaign. While Republicans could have a high level of confidence that McCain would win a straight popularity against Clinton, if the election is against Obama , or even John Edwards it is far less clear who would have the broader appeal.

Obama is literally a generation younger than McCain; Edwards is also much younger. A McCain-Clinton battle would inevitably be in large part about the past; a McCain-Obama, or McCain-Edwards fight would be about the future, and harder for McCain to win. This change in the Democratic lineup helps other republicans such as Giuliani.

The third factor that has changed for McCain since late last year is the war - but not in the obvious sense of its increasing unpopularity. The McCain advisers correctly say that there will not be much of a constituency in the Republican primary for an antiwar candidate. But the problem for the senator, the most fervent supporter of the war, is more subtle than that.

To his great credit, almost from the start of the war, McCain has publicly — and in private vociferously — criticized the Bush administration's conduct of the military struggle. From his first visit to Iraq in the months after the invasion, the senator has questioned the degree of commitment by the White House and the Pentagon.

This was not only, self-evidently, what McCain genuinely believed. It also provided the senator with a useful political opportunity. As the mess in Iraq got deeper, McCain could distance himself from the administration's execution of it. If only they had followed my advice to commit more troops, more effort, for longer, he could say, this would not have happened. As he put it at an American Enterprise Institute conference in December, if they are not going to do what is necessary in Iraq, it would be better if the United States was not there at all.

This gave McCain vital distance from an unpopular war. But when the administration changed tack in January and did commit more troops to the surge in Baghdad and elsewhere, McCain was in an awkward position. In his view, even this increased effort by President Bush may not be sufficient to win the war, but he has no alternative but to support it. Now he finds himself locked into a policy about which he himself continues to have doubts.

None of McCain's new problems is insurmountable. As Giuliani takes up the frontrunner position, he can be expected to come in for much more scrutiny from the media and critics. On the Democratic side, even if Clinton is in trouble, it is not obvious that McCain is an inferior candidate to either Obama or Edwards.

And the war, for all its failures and political perils, may still, paradoxically, represent the strongest case for voting for McCain. At a time when the United States is in grave international straits, its power threatened by enemies abroad and a loss of will at home, is there anyone better placed to lead the American people than someone with McCain's record?

If he can distance himself from the record of incompetent execution of the Bush administration and the crippling uncertainties of the Democrats, he has a compelling case to make. At least we can say, 10 months before the primary and 20 months before the general election, it's way too soon to count him out.