As Republicans take aim at Barack Obama's past links to a 1960s radical activist, some Democrats are threatening a tit-for-tat assault by noting John McCain's ties to a group that helped fund right-wing guerrillas during the 1980s Iran-Contra scandal.

The latest round of attacks came as the presidential hopefuls geared up for their second debate in Nashville tonight. With his fortunes fading in many key states, McCain has made no secret of his plans to question Obama's character – and Obama allies have fired right back.

After Republican No 2 Sarah Palin condemned Obama for attending a political event hosted by Bill Ayers, a former leader of the 1960s radical group the Weather Underground, Democratic pundits and bloggers began chiding McCain for his time on the board of the US Council for World Freedom (CWF).

The CWF was used as a conduit for arms sales and other aid to the Contras, a right-wing guerrilla group in Nicaragua that also got backing from the CIA under Ronald Reagan.

McCain was a congressional supporter of the Contras during the early 1980s, while serving on the CWF board but before the Iran-Contra scandal imperilled its work.

The CWF was affiliated with the World Anti-Communist League, whose chairman was forced to resign in 1980 after he was linked to the neo-Nazi movement. McCain joined the CWF the following year after meeting with its chief, former US army major general John Singlaub.

"I think I met him in the Washington area when he was just a new congressman," Singlaub told the Associated Press. "We had McCain on the board to make him feel like he wasn't left out. It looks good to have names on a letterhead who are well-known and appreciated."

The Obama campaign has yet to raise McCain's CWF connection directly, but prominent liberals are sure to continue raising the link as a way to temper Palin's Ayers-related attacks.

Democratic strategist Paul Begala, a former Bill Clinton adviser, was the first to warn McCain that condemning Obama's arms-length interactions could potentially backfire.

The timing of McCain's resignation – specifically, its proximity to the Iran-Contra scandal in 1986 – could become particularly pertinent. McCain has said he quit the group in 1984, and spokesman Brian Rogers told Politico.com that the Republican nominee resigned "when questions were raised about its activities".

"But that in no way diminishes his leadership role in ensuring that the forces of democracy and freedom prevailed in Central America," Rogers added.

McCain's name remained on CWF letterhead as late as 1986, however, according to several reports today.