(CNN) - Mitt Romney escalated his criticism of Newt Gingrich's temperament Wednesday, calling the former House speaker "zany" in an interview with The New York Times.
"Zany is not what we need in a president," Romney said, two days after he blasted Gingrich for his "erratic outspokenness."
In his sit-down with the newspaper, Romney said Gingrich's behavior served him well on the campaign trail, but would be disastrous in the White House.
"Zany is great in a campaign. It's great on talk radio. It's great in print, it makes for fun reading," Romney said. "But in terms of a president, we need a leader, and a leader needs to be someone who can bring Americans together."
Romney said his own nature would be better suited for a commander-in-chief.
"A leader needs to be someone of sobriety and stability and patience and temperance, to think through issues, to be careful in the choice of words he or she might express, because the world listens. The president of the United States is the leader of the free world, and our current president has been an enormous failure," Romney said.
Romney's "zany" appraisal is the latest ding on Gingrich's personality, which began in earnest Monday when the former Massachusetts governor called his slammed his rival's "erratic outspokenness" on Fox News. He was referring to Gingrich's remark that Palestinians were an "invented" people.
As the week progressed, Romney called Gingrich an "extraordinarily unreliable" conservative, pointing out inconsistencies in his record on Medicare and climate change.
Romney also hammered Gingrich for his role with mortgage giant Freddie Mac, demanding his competitor return the money he earned consulting for the company.
Gingrich returned fire, insisting Romney return money he made as an executive at Bain Capital, saying the company's work was responsible for "bankrupting companies and laying off employees.
Earlier Wednesday, Romney said Gingrich's claim revealed a certain degree of economic ignorance, saying on Fox News the former speaker "doesn't understand the economy if he doesn't understand that sometimes businesses succeed and sometimes fail."
Romney's campaign also circulated a video Wednesday of Gingrich saying in 2008 that anyone who profited from Fannie Mae and Freddie Mac's failure should return the profits.
"Everybody who was profiting from them should pay the cost of having failed. And the general taxpayer should not bear that burden," Gingrich is shown saying.
Romney said on Fox that Gingrich should abide by his own words.
"He said anyone who profited from Freddie Mac should give the money back. Well, he profited $1.6 million from an agency that helped bring down the entire economy; he ought to give it back," Romney said.
A second video Wednesday, produced by Romney's campaign, slams Gingrich for collaborating with fellow former House Speaker Nancy Pelosi on climate change solutions.
The video, which also tied Gingrich to former Democratic vice president Al Gore, underscores the campaign's message that Gingrich is an "unreliable leader."