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Newt Gingrich on Friday challenged GOP rival Ron Paul to explain more than a decade's worth of incendiary newsletters that he has disavowed.

The newsletters contain bigotry against black, Jews, and gays and an obsession with conspiracies.

"These things are really nasty, and he didn't know about it, wasn't aware of it," said Gingrich adding  "But he's sufficiently ready to be president? It strikes me it raises some fundamental questions about him."

Ron Paul has tried since 2001 to disassociate himself from the newsletters which starting in 1985 bore the name "Ron Paul Investment Letter", "Ron Paul Survival Report," and the "Ron Paul Political Report."

Paul this week told ABC News' Jon Karl that he "disavowed those messages" and added that he was practicing medicine at the time and that other people wrote part of the letters for him.

He even walked out of an interview on CNN on Wednesday claiming that he didn't write the newsletters.

But Paul has indicated that he knew of the newsletters as far back as 1995 and even vouched for the accuracy and admitted writing at least some of the passages in 1996.

During a bruising 1996 Congressional campaign, Paul's Democratic opponent Charles "lefty" Morris surfaced a 1992 newsletter which stated that 95 percent of black men in Washington "are criminal or entirely criminal."

Paul told the Dallas Morning News in 1996 that he was being taken out of context and the columns should be read in their entirety.

The 1992 newsletter also stated that "If you have ever been robbed by a black teenage male, you know how unbelievably fleet of foot they can be."

Paul did not deny to Dallas paper that he made the statement about the swiftness of black men.

"If you try to catch someone that has stolen a purse from you, there is no chance to catch them," Paul said.

Paul again vouched for a 1993 edition of the "Ron Paul Survival Report" addressed to "Dear Frightened American" warns of a "national emergency" when the government will close all banks and seize accounts to pay off debts, particularly for the war on drugs."

According to The Austin American Statesman, the newsletter went on to urge readers to buy foreign passports to better hide their assets from the federal government.

Paul countered at the time to the San Antonio Express-News that he has given readers of his newsletters legal and investment and personal security advice for some time.

"For Lefty to question the right of Americans to provide for their safety from terrorists and for financial security through legal means tells you where Lefty is coming from," Paul told the San Antonio Express-News.

Paul again in 1996 acknowledged that he wrote a 1992 newsletter that calls the late Barbara Jordan, the first black woman elected from the south to the U.S. House, a "fraud" and an "empress without clothes."

Paul told the Austin American Statesman paper he was contrasting Jordan's political views with his own.

"The causes she so strongly advocated were for more government, more and more regulations and more and more taxes," said Paul.

It wasn't until 2001 that Paul began to deny that the words in the newsletters weren't his, telling the Texas Monthly that others had written it because it was "too confusing."

"I could never say this in the campaign, but those words weren't really written by me," Paul said.

"It wasn't my language at all. Other people help me with my newsletter as I travel around."