(CNN) - Bob Dole, a Mitt Romney supporter and former Republican presidential nominee, issued a scathing statement Thursday blasting Newt Gingrich for being a "one-man-band who rarely took advice."

In an open letter to conservatives distributed by Romney's campaign, Dole said he personally took steps to assist the former House speaker pay off a penalty levied by the House Ethics Committee.

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"In 1997 a number of House members wanted to throw him out as Speaker," Dole wrote. "But he hung on until after the 1998 elections when the writing was on the wall. His mounting ethics problems caused him to resign in early 1999. I know whereof I speak as I helped establish a line of credit of $150,000 to help Newt pay off the fine for his ethics violations. In the end, he paid the fine with money from other sources."