Mitt Romney's son jokes about wanting to punch Barack Obama

Mitt Romney's eldest son Tagg told a radio station that the back-and-forth debate sniping between his father and Barack Obama made him want to "take a swing" at the president.

Asked in an interview with North Carolina radio host Bill LuMaye what it was like to sit through Tuesday's super-charged debate and hear Obama "call your dad a liar", Tagg Romney (pictured) said it made him want to "jump out of your seat and you want to rush down to the debate stage and take a swing at him".

He continued with his description of how the extraordinarily close race is weighing on those close to the protagonists.

He followed up his joke about punching Obama by saying: "But you know you can't do that because, well first because there's a lot of Secret Service between you and him, but also because it's just the nature of the process.

"They're going to try to do everything they can do to try to make my dad into someone he's not," Tagg, the eldest of Romney's five sons, said. "We signed up for it. We gotta kind of sit there and take our punches, and then send them right back the other way."

There was no malicious tone to his voice, and a campaign aide said on Thursday, the day after the remarks, that Romney was clearly speaking in jest.