The second presidential debate on Tuesday was a clash of finger-pointing, interruptions and bitter disagreements. Mitt Romney’s eldest son had an especially visceral reaction. Tagg Romney said his instinct was to “jump out of your seat” and “rush down to the debate stage and take a swing’’ at President Obama.

He was answering a North Carolina radio host, who asked how it felt to hear the president “call your dad a liar.’’

Tagg Romney quickly indicated he wasn’t speaking literally about striking the president.

“You know you can’t do that,’’ he continued, “because, well, first because there’s a lot of Secret Service between you and him, but also because this is the nature of the process. You know, they’re going to do everything they can do to try to make my dad into someone he’s not. We signed up for it. We’ve got to, kind of sit there and take our punches and then send them right back the other way.’’

The younger Romney’s remarks were indicative of how fiercely the campaign is being fought in its closing weeks. Although Tagg Romney, 42, the eldest of the five Romney sons, was reported to have assumed a prominent role in the campaign, even taking part in a family “intervention,” the picture he painted was of a far less significant player.

A spokeswoman for the campaign, Andrea Saul, said, “He was joking about how frustrating this process can be for family,” and in a television appearance on “The View” on Thursday, another Romney son, Josh, also said he didn’t mean it.

“The brothers have all made a pact not to give him advice,’’ Tagg Romney said of his father, speaking to Bill LuMaye on the North Carolina radio station WPTF-AM. “He’s getting advice from so many different angles. Our role is to go out and speak on his behalf and when we’re with him just to relax him and talk about anything other than politics to take his mind off it for a little while.’’

In the debate, the president did not outright call Mr. Romney a liar, though Mr. Obama did inject phrases on occasion like “what Governor Romney said just isn’t true” and “not true, Governor Romney.” Mr. Obama also said that Mr. Romney’s tax math “doesn’t add up,’’ accused him of having a “one-point plan” favoring the rich and, in a particularly heated moment, said to “get the transcript” after Mr. Romney denied the president called the Benghazi attack an act of terror.

As the final debate approaches, on Monday in Boca Raton, Fla., Tagg Romney mentioned how his father does get nervous before taking the stage. “He’s terrified before he gets out there!’’ he said, before quickly rephrasing his thought. “Terrified’s too strong a word. But you know, he’s like anybody — he gets butterflies a little bit,” he said. “And then once he’s in it, two or three minutes, he’s forgotten about the nervousness.’’