Three decades after abandoning his life as a fugitive, Bill Ayers has gone underground again.

The co-founder of the Weathermen, the anti-Vietnam War group that bombed the Pentagon and US Capitol in the 1970s, has vanished as John McCain seeks to make his links to Barack Obama a central issue in the last weeks of the presidential campaign.

There was no one home when The Times visited Mr Ayers' house in a quiet street three blocks from Mr Obama's mansion in the Hyde Park district of Chicago. The Education Department of the University of Illinois, where Mr Ayers works, said that he had gone on sabbatical. In response to an e-mail he stated: “I'm not available right now. Perhaps in the future. Best, Bill.” What The Times did find in Chicago, however, was widespread bemusement that Mr McCain should be putting so much emphasis on Mr Obama's tenuous links with Mr Ayers to revive his campaign.

Mr Ayers and his wife, Bernadine Dohrn, another Weathermen leader, emerged from hiding in 1980 and the charges against them were dropped because of prosecutorial misconduct.

Weatherman comes in from the cold

Although all charges against him had been dropped, Mr Ayers had remained in hiding with Miss Dohrn until today

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Since then he has become a respected member of Chicago's intellectual Establishment: a professor of education, author and champion of school reform. Ms Dohrn, mother of his two grown children, is an associate professor at Northwestern University.

Mr McCain invokes the Ayers connection repeatedly. He claims that “Mr Obama's political career was launched in Mr Ayers' living room”, and is broadcasting a campaign advertisement to that effect. Sarah Palin, his running-mate, accuses Mr Obama of “palling around with terrorists”.

The truth appears rather more prosaic. In 1995, as Mr Obama was preparing to run for an Illinois state senate seat, Mr Ayers and Ms Dohrn hosted a gathering to introduce him to local Democrats. Later the two men sat on the boards of two non-profit foundations. Mr Ayers once gave Mr Obama a $200 campaign contribution. Mr Obama once praised one of Mr Ayers' books on education but has condemned his acts of 40 years ago. There is no evidence they are close.

“This is Red-baiting like we haven't seen since McCarthy in the Fifties,” declared Nan Freund, Mr Ayers' neighbour for 25 years. “He's done a lot of good for education and for kids. They are wonderful neighbours. It's a ploy and it's going to get dirtier and dirtier as [the Republicans] fall farther behind.” “If you're new in politics and someone agrees to host a 'coffee' in their house so the candidate can meet people, get some volunteers and maybe some money it's very rare you'd refuse,” said Toni Preckwinkle, a black Democratic alderman [city councillor] for Hyde Park, who in other respects is quite critical of her party's nominee.

A more promising avenue for Republican investigators might be Mr Obama's eight-year career as a state politician that began with that “coffee” in Mr Ayers' house. Mr Obama seldom talks about that period, perhaps because it sits awkwardly with his image as a political reformer.

Critics say that the ambitious young senator became an astute practitioner of old-style politics and that, far from opposing Chicago's political machine, notorious for corruption and patronage, he embraced it. “I have seen no proof in Barack Obama's past that he's an agent of change or that he's a reformer,” said Delmarie Cobb, a Democratic political strategist from Chicago.

Mr Obama won a seat in the state senate in 1996 by the unorthodox means of having surrogates successfully challenge the hundreds of nomination signatures that candidates submit. His Democratic rivals, including Alice Palmer, the incumbent, were all disqualified. For Mr Obama's first six years as a senator the Democrats were the minority party, hampering his ability to push through legislation, but he learnt the political arts, joining a weekly poker school and took up golf as a means of networking. He collaborated in “redistricting” — the shameless redrawing of congressional districts for partisan advantage.

Critics suggest that political calculation may have influenced his decision to join the Trinity United Church of Christ, an African-American mega-church led by Jeremiah Wright, the fiery minister who subsequently married the Obamas, baptised their children and became his spiritual adviser. The church — 15 minutes south of Hyde Park — was favoured by the black intelligentsia. “It was a good church for an aspiring, upwardly mobile politician to join,” Ms Preckwinkle said.

If that was the reason, it backfired badly during this year's presidential primaries when a video showed Mr Wright accusing the US Government of creating Aids to kill blacks and shouting: “God damn America.” Mr Obama first stood by Mr Wright, then left the church. Mr Wright has also stood down.

The young senator also developed a close relationship with Tony Rezko, a Syrian-born property developer (and slum landlord) convicted in June on several corruption charges. The benefits were mutual. Mr Obama supported tax incentives for developers like Rezko to refurbish low-income housing. Rezko gave and raised money for Mr Obama's election campaigns. This friendship also backfired. In 2005 the Obamas bought their handsome Hyde Park home for $1.65 million — $300,000 less than the asking price — while Rezko's wife, Rita, simultaneously bought the vacant lot next to it from the same owner for the full price of $625,000. This raised suspicions that Rezko was either buying Mr Obama a bigger garden or helping to reduce the cost of the house. Even Mr Obama's supporters do not defend the malodorous arrangement. “He should never have allowed that to happen,” Barbara Flynn Currie, the local Democratic congresswoman, said. Mr Obama has admitted the deal was “boneheaded” and given Rezko's campaign contributions to charity.

In 2003 the Democrats won control of the Illinois senate and Emil Jones, a veteran of Chicago's political machine, became its president. Mr Obama courted him. Mr Jones was smitten. “Throughout 2003 and 2004 Jones offered Obama an array of high-profile Bills to shepherd through the senate,” David Mendell, a Chicago Tribune journalist, wrote in his biography of Mr Obama.

Those Bills gave Mr Obama a strong record on which to run for the US Senate in 2004. Mr Jones even scheduled legislative sessions around Mr Obama's campaign events. Critics contend that Mr Obama also avoided votes on controversial issues that might return to haunt him — “He was in the washroom on abortion votes,” commented a Democrat who requested anonymity.

The biggest disappointment for Hyde Park's liberal Democrats was Mr Obama's failure to oppose the political machine of Richard Daley, the powerful Mayor of Chicago, or to condemn its excesses and abuses. Indeed, he endorsed the mayor for re-election in 2007 even though Mr Daley's administration had suffered a string of indictments and corruption scandals. Weeks later Mr Daley reciprocated by backing Mr Obama for the Democratic presidential nomination.

Nobody accuses Mr Obama of acting illegally or — with the possible exception of his house purchase — even improperly during his Illinois years. His defenders argue, with justification, that he did what was required of any aspiring young politician with few connections in Chicago to succeed. Some Chicagoans, however, find his present efforts to portray himself as a champion of political change a little rich. “If you fail to speak out on issues that affect people here in Chicago, what would make me feel you're going to speak out for the American people on issues of substance when you become president?”, asked Ms Cobb, the strategist. “He's a very pragmatic person,” Ms Preckwinkle said, choosing her words with care.

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