The former president, who famously clashed with then-House Speaker Gingrich during Clinton's time in office, said that both Gingrich and Romney are hamstrung by what they believe they need to say to get the Republican nomination. 

"Neither one of them can say what they believe to be true and get nominated," Clinton said. "Romney's still trying to figure out what he did as governor of Massachusetts and still appeal to this driving vituperative energy."

A Democrat portraying Romney as a flip-flopper is nothing new, but one slapping the same label on Gingrich is a bit more rare. One of the biggest showdowns between Clinton and Gingrich came during chaotic negotiations over the federal budget that resulted in a government shutdown.