"Newt is the Wizard of Oz. ... there's nothing there. I think he has ginned up this whole big thing," Frank told ABC's "This Week" news program.
The Massachusetts Democrat said the former U.S. House speaker from Georgia would lose badly if he becomes the Republican candidate for president.
"He would be a very weak candidate. He would lose heavily and lot of Democrats would win races in which there would be a great fall-off. I think Newt Gingrich is the anti-candidate -- the split between the extremely conservative sector of America, which is the Republican presidential primary electorate, and the rest of the country, is very clear."
Frank, who announced this week he will not be seeking a 17th term in the House of Representatives, said Gingrich has a number of vulnerabilities that contribute to him being a weak candidate, including being "twice reprimanded by the House," "the problem with the marriages," and that he may just be a nominee that is not Mitt Romney.
"And I believe that a man with Gingrich's vulnerability -- if he wins the nomination it will be because Mitt Romney is understandably seen as insufficiently conservative, because Mitt insufficiently anything, if you believe in principles. And that will allow Gingrich to overcome a whole lot."
Also on "This Week," Republican presidential hopeful Rick Santorum, a former U.S. senator from Pennsylvania, said he will continue his campaign, despite lagging poll standings.
"If you look at every poll, we keep moving up, moving up slowly. But we're within the margin of error of both [Texas Gov.] Rick Perry and [U.S. Rep.] Michele Bachmann [R-Minn.], both of whom have had enormous attention by the national media, and have had money and resources," he said.
"We think we're going to do very, very well. We have a very strong, consistent conservative message that matches up better with Iowans than anybody else. And we think we're going to surprise a lot of people."
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