"60 Minutes" relied on the documents as part of a segment last week — reported by CBS News Anchor Dan Rather — on Mr. Bush's service in the Texas Air National Guard from 1968 to 1973.
Also featured in the segment was former Texas Lt. Gov. Ben Barnes, a Democrat who claims he pulled strings to get Mr. Bush into the Guard in 1968. At that time, membership in the Guard made service in Vietnam unlikely.
Questions have been raised for years about Mr. Bush's entry into and service in the Guard. Of particular interest has been a period from mid-1972 to mid-1973 for which there is conflicting evidence Mr. Bush performed his duties. It is known that he missed a flight physical during that time.
The White House contends Mr. Bush received no favorable treatment and fulfilled his duties.
The documents in question are memos that carry the signature of the late Lt. Col. Jerry Killian, who was the commander of Mr. Bush's Texas Air National Guard fighter squadron. They say Killian was under pressure to "sugar coat" Mr. Bush's record, and that Mr. Bush refused a direct order to take the required medical examination and discussed how he could skip drills.
Since the 60 Minutes broadcast, news organizations, conservative critics and bloggers have questioned the authenticity of the documents, pointing to type styles that seem the product of a modern computer rather than a 1970s-era typewriter. Relatives and fellow officers of Killian have also said they doubt the documents are real.
CBS says it stands by its story. The network has not revealed how it obtained the documents.
On Monday's CBS Evening News, Rather said his original report used several different techniques to make sure the memos were genuine, including talking to handwriting and document analysts and other experts who strongly insist that the documents could have been created on a typewriter in the 1970s – as opposed to a modern-day word-processing software program, as some have charged.
"Everything that's in those documents, that people are saying can't be done, as you said, 32 years ago, is just totally false. Not true. Proportional spacing was available. Superscripts were available as a custom feature. Proportional spacing between lines was available. You can order that any way you'd like," said document expert Bill Glennon.
Richard Katz, a software designer, found some other indications in the documents. He noted that the letter "L" is used in those documents, instead of the numeral "one." That would be difficult to reproduce on a computer today.
In addition to the forensic evidence, Monday's Evening News story said the original report relied on an analysis of the contents of the documents themselves and interviews with colleagues of the author to determine their authenticity. The new papers are in line with what is known about the president's service assignments and dates.
For instance, the official record shows that Mr. Bush was suspended from flying on Aug. 1, 1972. That date matches the one on a memo given to CBS News, ordering that Mr. Bush be suspended.
But other media organizations have questioned different aspects of the documents and the 60 Minutes piece.
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" Mr. Bush's record had left the Texas Air National Guard 1½ years 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.
New York Times columnist William Safire wrote Monday that Newsweek magazine had apparently begun an external investigation: it names "a disgruntled former Guard officer" as a principal source for CBS, noting "he suffered two nervous breakdowns" and "unsuccessfully sued for medical expenses."
The L.A. Times reported that handwriting analyst, Marcel Matley, who CBS had claimed vouched for the authenticity of four memos, vouched for only one signature, and no scribbled initials. The Times reports he has no opinion about the typography of any of the supposed memos.
The Washington Post on Tuesday catalogued a number of doubts about the documents, including factual problems like an apparently outdated address for Mr. Bush on one document, differences in typing style between the newly broadcast documents and others from the Texas Air National Guard, and examples of incorrect military lingo.
The New York Times reported that some CBS News employees are growing increasingly worried over the questions about the documents.
On Tuesday, Mr. Bush told a National Guard group that he was proud of his time in the Texas Air National Guard, but he did not address the dispute about his service three decades ago.
"Nineteen individuals have served both in the National Guard and as president of the United States,'' Mr. Bush told the National Guard Association of the United States in Las Vegas, "and I'm proud to be one of them."
First lady Laura Bush said Monday that she thought the documents obtained by CBS were probably fakes.
"You know, they probably are altered and they probably are forgeries, and I think that's terrible, really," she told Radio Iowa in an interview.
White House spokesman Scott McClellan said the White House was not investigating the documents, but that "serious questions" were being raised "and they should be looked into" by the media.
Former colleagues of Killian have offered differing views on the authenticity of the documents.
Robert Strong, who appeared in the original segment, said after it aired that still did not see anything in the memos that made him think they were forgeries. Robert Strong noted he's not a forensic expert and isn't vouching for the documents.
"I didn't see anything that was inconsistent with how we did business," Strong said in an interview. "It looked like the sort of thing that Jerry Killian would have done or said. He was a very professional guy."
Retired Col. Maurice Udell, the unit's instructor pilot who helped train Mr. Bush, said Friday he thought the documents were fake.
"I completely am disgusted with this (report) I saw on 60 Minutes,"' Udell said. "That's not true. I was there. I knew Jerry Killian. I went to Vietnam with Jerry Killian in 1968."
Killian's son also questioned some of the documents, saying his father would never write a memo like the "sugar coat" one.
Several of the document examiners said one clue that the documents may be forgeries was the presence of superscripts — in this case, a raised, smaller "th" in two references to Guard units.
But Katz, the software expert, pointed out that the documents have both the so-called "superscript" th (where the letters are slightly higher than the rest of the sentence, such as 6th ) and a regular-sized "th". That would be common on a typewriter, not a computer.
"There's one document from May 1972 that contains a normal "th" on the top. To produce that in Microsoft Word, you would have to go out of your way to type the letters and then turn the "th" setting off, or back up and then type it again," said Katz.