Fresh doubts have surfaced on the authenticity of memos on US President George W Bush's military record.
Doubts about Mr Bush's service were first raised in the 2000 election
The documents say Mr Bush was suspended from flying for the Texas Air National Guard during the Vietnam war because he failed to meet its standards.
In the latest twist, the secretary who would have typed the memos said they appeared to have been forged.
However, Marian Carr Knox told CBS television - which first broke the story - that the content was truthful.
With national security a key issue in the US presidential elections on 2 November, supporters of Mr Bush and Democratic nominee John Kerry have been attacking each candidate's Vietnam records.
Republicans have attacked Mr Kerry's war service and Democrats have accused the president of ducking the draft call in favour of less dangerous duties.
Last week, CBS reported that it had obtained documents from Mr Bush's late Texas commander, saying Mr Bush discussed with him how to avoid drills during 1972.
In a memo, Lt Col Jerry Killian, who died 20 years ago, also said he was being pressured from his superior to give Mr Bush a positive evaluation.
But his secretary told CBS Evening News on Wednesday: "I know that I didn't type them."
Kerry's aides deny any links to the records
"However, the information in those is correct," Ms Knox said.
CBS News president Andrew Heyward said in a statement: "I'm very confident in the report, but I want to get to the bottom of these continuing questions."
Correspondents say the row over the authenticity of the documents has distracted attention from their contents.
After CBS obtained the documents, the White House released its records showing Mr Bush's suspension also resulted from his failure to take his annual medical test as required.
Mr Bush trained as a pilot while a member of the Texas and Alabama air national guard but never flew in combat.
Documents already released by the White House show that Mr Bush was suspended from flight status in 1972 for not having a medical test - but do not mention his alleged failure to comply with national guard standards.
Some forensic experts have said the memos appear to have been computer-generated with characteristics that were not available three decades ago.