If Republicans nominate Newt Gingrich, "it will have an adverse impact on Republican candidates running for county, state, and federal offices," former Senate Republican Leader Bob Dole, the GOP's 1996 presidential nominee, said in an "open letter" Thursday.

"Hardly anyone who served with Newt in Congress has endorsed him and that fact speaks for itself. He was a one-man-band who rarely took advice. It was his way or the highway," Dole said.

Dole was Senate leader while Gingrich was House Speaker from 1995 to 1999.

Dole recalled Gingrich's $300,000 penalty for ethics violations. "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," Dole said.

He also blasted Gingrich's intellect.

"Gingrich had a new idea every minute and most of them were off the wall.  He loved picking a fight with Bill Clinton because he knew this would get the attention of the press," Dole recalled.

"In my run for the presidency in 1996 the Democrats greeted me with a number of negative TV ads and in every one of them Newt was in the ad.  He was very unpopular and I am not only certain that this did not help me, but that it also cost House seats that year.

"Newt would show up at the campaign headquarters with an empty ice-bucket in his hand—that was a symbol of some sort for him—and I never did know what he was doing or why he was doing it.

"In my opinion if we want to avoid an Obama landslide in November, Republicans should nominate Governor Romney as our standard bearer. He has the requisite experience in the public and private sectors. He would be a president we could have confidence in."