Stephen Morton/Getty Images; Steve Pope/Getty Images

Mitt Romney has a new word to describe the man who has now eclipsed him in the polls: zany. That's how he described Newt Gingrich in an interview Wednesday with the New York Times before cautioning that "zany is not what we need in a president."

"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."

This is the latest in the stream of attacks the Romney camp has launched at Gingrich this week. He has also called Gingrich an "extraordinarily unreliable leader" and blasted him for not being able to handle negative ads, saying "there's no whining in politics."

"He's a great historian," Romney said of Gingrich. "If we need a historian leading the country, I'm sure people would find that attractive. I actually think you need someone who actually understands the economy leading the country."

Gingrich has come under the microscope lately for some of his out-of-the-mainstream ideas such as creating colonies on the moon to mine lunar minerals, reforming child labor laws so school children can work as janitors and establishing a defense system against an electromagnetic pulse attack.

Romney told the Times that his campaign's attempts to draw distinctions between the two candidates is working.

"People are taking a closer look at Speaker Gingrich," Romney said. "And like other people who bumped up in the polls in this last year, as they take a closer look, some are happy with what they see and some would like to see something else and recognize that he may not be exactly what they wanted."

Romney's interview with the Times is his fifth major news interview this week as he trades sweeps through early primary states for swings through network newsrooms .

Romney is expected to sit down with Jan Crawford on "CBS Evening News" tonight.