The memos seem to show President Bush's National Guard commander believed Mr. Bush at times shirked his duties and used his political influence.
The network is adamantly defending the authenticity of the memos, saying experts who examined the memos concluded they were authentic documents produced by Mr. Bush's former commander, Lt. Col. Jerry Killian. CBS News added that contemporary colleagues of Killian also believed the memos were genuine.
On Saturday, there were reports that retired National Guard Maj. Gen. Bobby W. Hodges - who corroborated the CBS News account - now says he believes the documents were not real, in part because of recent statements of Jerry Killian's relatives.
CBS News responded, saying, "We believed General Hodges the first time we spoke with him. We believe the documents to be genuine. We stand by our story and will continue to report on it."
Casting further doubt on the memos, The Dallas Morning News said in a report for its Saturday editions that the officer named in a memo as exerting pressure to "sugar coat" Bush's record had left the Texas Air National Guard 18 months before the memo was dated.
The newspaper said it obtained an order showing that Walter B. Staudt, former commander of the Texas Guard, retired on March 1, 1972. The memo was dated Aug. 18, 1973. A telephone call to Staudt's home Friday night was not answered. Other obersevrs noted that Staudt could have remained active and influential in National Guard affairs after his formal retirement.
Saturday's edition of the Boston Globe reports that one document expert, Philip Bouffard, who had expressed suspicions about the documents, said "he now believes the documents could have been prepared on an IBM Selectric Composer typewriter available at the time."
Anchor Russ Mitchell of the Saturday edition of the CBS Evening News says CBS News contacted Bouffard Saturday, and Bouffard said he could not dismiss the documents as fake, but he needs to do more analysis before coming to a final conclusion.
In a report on Friday night's "CBS News Evening News," Dan Rather noted that many of those raising questions about the documents have focused on something called superscript, a key that automatically types a raised "th."
Critics claim typewriters didn't have that ability in the 1970s. But some models did, Rather reported. In fact, other Bush military records already released by the White House itself show the same superscript – including one from as far back as 1968.
Some analysts outside CBS News say they believe the typeface on these memos is New Times Roman, which they claim was not available in the 1970s.
But the owner of the company that distributes this typing style told CBS News that it has been available since 1931.
In a statement Friday, CBS News said it stands by its overall story.
"This report was not based solely on recovered documents, but rather on a preponderance of evidence, including documents that were provided by unimpeachable sources, interviews with former Texas National Guard officials and individuals who worked closely back in the early 1970s with Colonel Jerry Killian and were well acquainted with his procedures, his character and his thinking," the statement read.
"In addition, the documents are backed up not only by independent handwriting and forensic document experts but by sources familiar with their content," the statement continued. "Contrary to some rumors, no internal investigation is underway at CBS News nor is one planned."
Document and handwriting examiner Marcel Matley analyzed the documents for CBS News. He says he believes they are real. And he is concerned about exactly what is being examined by some of the people questioning the documents, because deterioration occurs each time a document is reproduced. And the documents being analyzed outside of CBS News have been photocopied, faxed, scanned and downloaded, and are far removed from the documents CBS News started with.
Matley did an interview with "60 Minutes" prior to Wednesday's broadcast. He looked at the documents and the signatures of Col. Killian, comparing known documents with the colonel's signature on the newly discovered ones.
"We look basically at what's called significant or insignificant features to determine whether it's the same person or not," Matley said. "I have no problem identifying them. I would say based on our available handwriting evidence, yes, this is the same person."
Matley finds the signatures to be some of the most compelling evidence.
Reached Friday by satellite, Matley said, "Since it is represented that some of them are definitely his, then we can conclude they are his signatures."
Matley said he's not surprised that questions about the documents have come up.
"I knew going in that this was dynamite one way or the other. And I knew that potentially it could do far more potential damage to me professionally than benefit me," he said. "But we seek the truth. That's what we do. You're supposed to put yourself out, to seek the truth and take what comes from it."
Robert Strong was an administrative officer for the Texas Air National Guard during the Vietnam years. He knew Jerry Killian, the man credited with writing the documents. And paper work, like these documents, was Strong's specialty. He is standing by his judgment that the documents are real.
"They are compatible with the way business was done at that time," Strong said. "They are compatible with the man I remember Jerry Killian being. I don't see anything in the documents that's discordant with what were the times, the situation or the people involved."
Killian died in 1984.
Strong says the highly charged political atmosphere of the National Guard at the time was perfectly represented in the new documents.
"It verged on outright corruption in terms of the favors that were done, the power that was traded. And it was unconscionable from a moral and ethical standpoint. It was unconscionable," Strong said.
The president's service record emerged as an issue during the 2000 race and again this winter. The Killian documents revived the issue of Mr. Bush's time in uniform after weeks in which Democratic challenger John Kerry, a decorated Vietnam combat veteran, has faced questions over his record as a Navy officer and an anti-war protester.
The questions about Mr. Bush's service center on how Mr. Bush got into the Guard and whether he fulfilled his duties during a period from mid-1972 to mid-1973.
What the Killian memos purport to show is that Mr. Bush defied a direct order to appear for a physical exam, that his performance as an officer was lacking in other ways and that Mr. Bush used family connections to try to quash any inquiry into his lapses.
In a separate development, the Boston Globe this week reported that Mr. Bush promised to sign up with a Boston-area unit when he left his Texas unit in 1973 to attend Harvard Business School. Mr. Bush never signed up with a Boston unit.