CBS is aggressively defending the documents it obtained about President George W. Bush's time in the Texas Air National Guard are authentic, but others aren't so sure.

Newly unearthed memos indicate that Bush ignored an order from a superior officer, and ultimately lost his pilot status because he failed to meet standards and undergo a medical exam.

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PDF: Memos About Bush's Service
Timeline: Bush's National Guard Service

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CBS, which originally reported on the memos, is standing by them. The documents were vital in the "60 Minutes II" report on Bush's service from 1968 to 1973.

"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 Col. Jerry Killian and were well acquainted with his procedures, his character and his thinking," the company said in a statement.

"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 said. "Contrary to some rumors, no internal investigation is under way at CBS News, nor is one planned. We have complete confidence in our reporting and will continue to pursue the story."

But some say the documents are forgeries. Some experts quoted by The Associated Press and other news organizations say the memos had features unavailable in the early 1970s when they were supposedly written.

One independent document examiner said it looks to her as if they came from a computer using Microsoft Word software and not a Vietnam-era typewriter.

She points to the superscript "th" in "111th Fighter Interceptor Squadron" as evidence. Those letters are inserted in the documents CBS obtained in the exact style as they would be in a Microsoft Word document, the expert said.

But CBS insists the marks were available on typewriters used at the time.

The son of Lt. Col. Jerry Killian, who reportedly wrote the memos, said he doubts they are authentic.

Gary Killian said one paper with his father's signature appears legitimate, but he said another -- in which his father says he was under pressure to "sugar coat" Bush's performance -- seems fake.

The White House says it doesn't know if the memos are genuine, but a spokesman said this much is clear: Democrats are "determined to throw the kitchen sink" at the president.

Press Secretary Scott McClellan said regardless of where the documents came from, they don't change the fact that Bush did his Vietnam-era duty and was honorably discharged.

McClellan said it's all part of an "orchestrated effort" by Democrats to tear down Bush because John Kerry is slipping in the polls.

But Democratic National Committee chairman Terry McAuliffe said Americans "deserve to know the truth" about Bush's time in the Texas Air National Guard.

McAuliffe wants Bush to publicly answer questions about his Vietnam-era service.

He said that even if those particular records turn out to be fakes, there's other evidence the commander-in-chief shirked his duty in his early days. He said Pentagon documents show Bush "just didn't show up." McAuliffe said Bush has twice lied about his military service.