Going into the first presidential debate two weeks ago, President Bush's campaign aides were so confident their candidate was in the ascendant that they quietly hoped that, with a strong performance, he might in effect finish off John Kerry's presidential ambitions that night.

What a difference a fortnight makes.

The dynamic of the US presidential election has shifted so much after the first two debates that, going into last night's final confrontation between the two, it was the Kerry people who were saying that a third and final debate victory for the Democrat would doom President Bush.

It didn't quite work out that way. The two men battled hard again, somewhat more politely this time than in the previous debates, even ceasing fire from time to time to pay each other compliments. Mr Kerry seemed more in command, although Mr Bush was probably the more engaging and personable.

There was no knockout blow for either side; instead it looked like a small Kerry advantage; a subjective verdict quickly confirmed by the TV networks' instant polls. That in itself, given the way the contest is currently moving, is not good news for Mr Bush.

The President needed a strong performance in Tempe, something that would halt the momentum of Mr Kerry's campaign, which has gone from a 6 point deficit in the opinion polls two weeks ago to a tie this week, with a growing number of polls now showing the Massachusetts senator moving into a small lead.

This debate was supposed to be about domestic issues; and the two candidates tussled over jobs, taxes, health care, abortion and gay rights. But the Iraq war was never far from the discussion, whether in the context of homeland security or the possibility of reinstating conscription.

The challenge for Mr Bush was to land really effective blows on his opponent, while at the same time maintaining the dignity and stature of the presidential office.

In the end both sides traded now very familiar blows. There were repeated recitations of stock phrases and arguments from previous debates and the campaign trail. Mr Kerry's 98 votes in the Senate for tax increases; Mr Bush's record as the first incumbent to preside over net job losses during his term in 70 years.

Mr Bush insisted that Mr Kerry's voting record over 20 years in the Senate out him out of the mainstream of American politics and on "the left bank". Mr Kerry landed effective blows, especially on the Bush jobs record, which is, by historic standards, not good.

But oddly, given that he is the incumbent, Mr Bush again seemed to lose the battle to look the more presidential. He was not scowling and shifting as he did in the first debate (and he got in quite a good self-deprecating joke about it), but he did offer a few distinctly unstatesmanlike utterances in response to what he considered implausible statements by his opponent..

How much impact this third meeting will have had on voters is hard to gauge, but the answer is probably not much. There was, for many viewers, one suspects, a lot of quite tedious legislative details, with contesting views about compounding interest rates and Pay as You Go rules and obscure Senate votes from the early 1990s.

But if voters were left mostly unmoved by the debate, that again is probably bad news for Mr Bush. Time is running out for him to reverse Mr Kerry's powerful momentum.

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