There seems to be a certain inevitability about US presidential elections descending from the question of which candidate has the better character, to which candidate has the better resources for character assassination; and indeed, that now seems to be the test between the rival camps of John McCain and Barack Obama on the eve of the October 7 presidential candidates' debate.

Ahead of the 2000 Republican presidential nomination, the George Bush camp obliterated McCain with a move that, among other things, invoked racism by alleging that McCain's adopted daughter from Bangladesh was a product of supposed inter-racial infidelity by McCain. The 2004 Republican campaign against the Democrats' John Kerry gave "swift boating" to the parlance of electioneering in the US by seeking tarnish Kerry's war record in Vietnam. These are not the only examples, and dirty fighting by no means has been the preserve of Republicans.

While some in the media are portraying the debate scheduled for October 7 at Belmont University, Nashville, as a make-or-break event, it should not be hyped up in isolation. With less than a month to go to the elections on November 4, every hour counts - and on the internet and in the broadcast media, every minute that could win either camp a "breaking news" item or a top-rated internet item. The most appropriate measure for the pace of presidential campaigns should be bytes per second.

The debate will provide a focal point, but the story is running apace, and now has turned to the respective campaigns' negative messages. The Republicans have gone bare-knuckle, with the Sarah Palin "pally with terrorists" message against Obama about his supposed relationship with Bill Ayers (a character in search of an adjective - depending on which ideological corner of the internet you visit, Ayers is everything from an "activist" to a "terrorist" to an "unrepentant terrorist"; on rare occasions, he's just a professor).

There has been extensive reporting that the Ayers move, which in any case is a revival of a much earlier stab by Hillary Clinton and others against Obama, is a deliberate attempt by the Republicans to distract attention from the economy and bring into question Obama's character. Another prong of this campaign is the Republican National Committee's request for an inquiry into breaches of regulations in the acceptance by the Obama camp of some campaign donations.

Once a campaign goes down this road, there is no turning back. The McCain-Palin camp will not be offering sunlight and sweetness to the sunlit uplands and a thousand points of light. Expect to hear about the heart of darkness, the one that beats in the breast of the junior senator from Illinois.

Obama's lot are not being angels, either. Until now, it has been fairly gentle stuff. Trying to tie McCain to the pair of concrete socks that is the two terms of George W Bush; portraying McCain as out of touch on the economy; drawing attention to the actuarial vulnerabilities of McCain, to wit, his age and his health.

Now, the Obama camp is to portray McCain as "erratic in judgment" with a campaign ad also to be available online, and is raking up the Keating Five story, the 1989 episode around the Savings and Loan scandal which led to McCain having been one of five senators investigated for alleged corruption, and which saw McCain having deemed by a senate ethics committee to have shown "poor judgment". Of course, if the mainstream media do not take the bait - which to an extent they will do, having allowed the story to become about Ayers and taking their eyes off the financial crisis ball, falling neatly and collectively into the Republican trap - then they will be accused of "liberal bias".

Nothing is out of play as the viciousness grows. Right-wing bloggers have point-by-point analyses online supposedly demonstrating the "bias" against Palin by Gwen Ifill, moderator of last week's vice-presidential debate.

It may be regrettable that both camps will, to varying degrees, resort to character assassination. With the domestic economy certain to remain top of concerns between now and the election, US voters are likely to be much more keen to know who would be the best candidate to lead the country into the post-bailout future, rather than be distracted by supermarket-tabloid-level smears.

At least some of those who tuned into the Palin-Biden debate may have hoped for some entertainment from gaffes by Palin; but expectations for the Obama-McCain debate should be different, given that neither domestic nor foreign policy now offer any scope for laughing matter. The US cannot be led out of crisis on the basis of the winning candidate being the one more skilled at character assassination.

But there seems faint hope of that. In the short time it has taken to bash out this blog on my keyboard, a pile of new items have been posted on the `net smearing Obama. The polls may currently show Obama in the lead (right-wing conspiracy theorists suggest that these polls are manipulated by the same mainstream media) but it is an open question whether the debate will leave the race anything other than effectively still too close to call.

• The presidential debate is at 9pm US Eastern Time; thus 4am Eastern European Time for viewers in Bulgaria; and for those unfamiliar with either time zone as a frame of reference, 1am GMT.