Mitt Romney aggressively criticized rival Newt Gingrich on Tuesday, calling the former House speaker a “lifelong politician” and questioning Gingrich’s ability to fix the country’s struggling economy.

Romney, speaking a day after Gingrich criticized him during a campaign stop in South Carolina, told Fox News that Gingrich wasn’t as likely to beat President Barack Obama in a general election.

“I think to get President Obama out of office, you’re going to have to bring something to the race that’s different than what he brings. He’s a lifelong politician,” Romney said of Gingrich. “I think you have to have the credibility of understanding how the economy works. And I do.”