I believe it was Michael Kinsley who said that a gaffe is when a politician inadvertently tells the truth:
Downing Street moved swiftly to play down an apparent admission by British Prime Minister Tony Blair that the invasion of Iraq had been a "disaster," labelling his comments a "slip of the tongue."
In an interview Friday on Al-Jazeera's new English-language channel, broadcaster Sir David Frost suggested that the 2003 US-led and British-backed invasion had "so far been pretty much of a disaster." ...
But during Blair's trip to Pakistan for talks with President Pervez Musharraf, the prime minister's official spokesman told reporters: "It was a straightforward slip of the tongue... sometimes he does this when he's half-listening to the question and wants to get on and respond."
The spokesman insisted that Blair did not think Iraq was a disaster.