One rule of the Democratic death dance is that everything that hath been done to a candidate by others, shall be done by him or her – okay, her – to the current opposition. Weeks ago, both Obama and Hillary seemed capable of holding to some line on charges and insults, that wouldn’t actually give the Republicans ammunition come the contest proper – which, at the current rate, will be squeezed into the last week of October.

By common consent Hillary broke that one with her suggestion that McCain would make a better commander-in-chief than Obama, and that the latter was essentially unqualified to lead. Though the Obama team is now getting a press backlash for having been treated too favourably by the, erm, press, there’s no doubt that he has run a cleaner campaign, and one more loyal to the Democrats as a party, than the Clintons whose party loyalty is to The Clintons.

But is that restraint out of genuine solidarity to the cause and a desire to rise above? Or is it out of diffidence, a process of being caught off-guard by the fixtures-and-fittings assault he has been subject to? Or is it because the attack hasn’t been the full catastrophe – that there is still a line both sides are refusing to cross because they know it would utterly sink the party come November, insofar as it isn’t listing dangerously already?

After all, if Obama really wanted to tear the joint up, he could really draw a line under the old politics and the new, and pretty much crucify the Clintons for squandering the hope of the Democratic party in the 90s through their combination of insular politics, their association with trash like the amoral political fixer Dick Morris, Monicagate and if he had nothing left to lose, Whitewater.

He could really sheet home the idea that if the Clintons got control of the party levers again, then it wouldn’t matter who won in November – essentially returning Clinton’s McCain favour – the old politics would be in charge again. Wouldn’t such a burst of evil energy be exactly the sort of thing he needed to get his teeth back on Hillary’s throat?

Maybe he’s waiting to use it later rather than sooner – or maybe he just can’t afford to escalate things further. For however centrist his policies now are, Obama’s from the left, and the sort of left that, while perfectly acceptable as a heritage in the UK (eight members of Blair/Brown’s inner cabinets have been ex-Communist party members, including three home secretaries), and pretty much compulsory in Italy, is out of the question in the US.

By his own account, Obama came out of the postmodern student left, talking of postcolonialism, discourse and oppression at the ironically named Occidental college in California. But that is less relevant than his years as a community organiser in the south side of Chicago (the baddest part of town), a crossroads for a wide variety of causes and activists – old leftists, black separatists, radical liberals and grassroots anti-globalists.

Obama was bound to come in contact with some people who’d make Nader look like Mitt Romney’s straighter brother, and the Right has already tested the waters with stories about Obama’s several connections with Bill Ayers and Bernadette Doehn, two of 60s urban guerrilla group The Weathermen who subsequently became non-violent activists.

The earliest reports were that Obama and the two had had a few meetings in the mid 90s, and Obama was required to clarify that he didn’t advocate bombing the Capitol building as a way of registering dissent. More meetings have emerged – appearing together on a discussion panel, Ayers and Obama speaking at a testimonial dinner for a pretty-hard core Muslim activist, and maybe more to come.

Caught up in the chaos of the earlier part of the primary season, when there were still a half-dozen candidates in the mix, no-one battened on to the issue – in part because there were other, more recent people to hammer Obama with, such as the endorsement of Nation of Islam leader Louis Farrakhan. Explaining The Weathermen involves a pretty substantial history lesson for a nation for whom everything before season one of Seinfeld is a misty haze, and also reminds people that Islamists aren’t the only ones who use bombs.

But there’s no doubt it will come back hard in the campaign proper – and that Hillary would be on it in a second if she wasn’t more or less thought of as being Patty Hearst herself. What she may be more keen on is leaning on Obama’s association with his pastor, Jeremiah Wright of the Trinity United Church, who runs a pretty standard fire-and-brimstone white Amerika is the great satan sort of line.

Like everything in Obama’s life, his membership in this church is less out of deep compulsion than in the ongoing process of putting together an identity – as he himself notes, he needed a community, a context, to be part of when he arrived in the Windy City. He doesn’t mean this in a cynical, become Collingwood-number-one-ticket-holder sort of way – but nor was it a sudden, divine calling sort of thing.

Hillary will be steering clear of making a demand for Obama to condemn and renounce his pastor, as she’s busy apologising to black voters for Geraldine Ferraro’s comments about Obama getting an easy ride. But she may swing round for it in a couple of weeks. And if she doesn’t then John McCain – who was in a prison camp while The Weathermen were taking his captors’ war to the American heartland – will open the whole thing up for the duration, in a post 9/11 world not so generously disposed towards the struggle against the military-industrial complex.