'I don't regret setting bombs', says Obama's friend

Atlanta: Barack Obama has a problem with one of his pals: an avowed ex-terrorist who never faced trial, never repented and regrets the crimes he didn't get a chance to commit.

Keep in mind that Obama's campaigning to become commander-in-chief of the global war on terror, so it's a tiny bit awkward.

Obama lost this week's primary in Pennsylvania with no hint that his old friend Bill Ayers had hurt him, but wait. It's a heck of a story and no doubt we'll all be hearing more of it.

Ayers is now a professor who lives in Obama's neighbourhood in Chicago. Back in the tumultuous 1960's and 1970s Ayers was part of a US terror group called the Weathermen.

It was so long ago, that some Americans have to be reminded that it wasn't a meteorology club. It took its name from a Bob Dylan lyric that "you don't need a weatherman to tell which way the wind blows".

Violent group

But they weren't just hippies with a taste for folk music. The Weathermen bombed government offices and killed innocent people.

Ayers was deeply involved. He acknowledges taking part in bombings at New York City's Police Headquarters, the Washington Capitol building and the Pentagon.

He escaped trial because misconduct by a prosecutor ruined the government's case, but his past is no secret. He wrote a book about it and told The New York Times: "I don't regret setting bombs... I feel we didn't do enough." That particular remark was published on September 11, 2001 - the day of those other terror attacks on the US. Like I said, it's awkward.

In 1995, as Obama was beginning his political career with a run for the Illinois state senate, he held a campaign meeting in Ayers' home. He's also worked with Ayers overseeing a local community organisation and his campaign manager described them as "friendly."

When Ayers' name came up during a recent televised debate, Obama said: "the notion that me knowing someone who engaged in despicable acts 40 years ago when I was 8 years old, somehow reflects on me and my values doesn't make much sense".

Hillary Clinton mentioned Ayers as the kind of weakness that can defeat the Democrats if they choose Obama as their candidate.

The Republicans have been pretty quiet.

It's almost like Ayers is such good ammunition, they're saving it until they need it and they know it's really going to hurt.

Jonathan Mann is a reporter and anchor for CNN International