A split second of misjudgement on his part will affect him for weeks to come.
Be it in the company of a journalist, a photographer or a television crew, MPs often have seconds to decide how to react to a loaded question, or a request to don a comedy hat. What would Blair have done if asked about past lovers? He probably would have blushed scarlet, buying time with mock-shock before announcing: 'Thousands, millions of grateful females.' Problem extinguished.
And yet Blair's wife fell foul of these glitches often. In 2003, as police confirmed the body found on Harrowdown Hill was that of Dr Kelly, Cherie was in Beijing belting out the McCartney hit When I'm 64. A photographer next to her at the time says: 'It was a hard call, the pupils were shouting for the PM to sing. When he refused and said his wife was "the singer" they started chanting for her and handed her the microphone. What was she to do?'
Gordon Brown has hired himself a gaffe-slayer, Nicola Burdett, to stop the embarrassing photos and TV footage that have left him looking grumpy and silly. He chose not to touch the Olympic torch at the weekend, but that was predictable - it is the unexpected slips that are the most damaging. They happen so easily.
In 2002, Tory MP David Willetts visited a homeless drop-in centre; he sat down beside an elderly homeless man happy with the surrounding media. The cheerful man began to play Down at the Old Bull & Bush with a pair of silver spoons, producing another set for Willets to join in. Willetts froze; it was buttock-clenching, but funny.
In 2005, then Tory leader Michael Howard found himself in prime discomfort territory - a school visit. During one hour he had to eat a cream bun; fend off a googly from an eight-year-old and in a tailored suit play a life-size game of Jenga. It was all rather Gilbert & George.
And just last week, Children's Secretary Ed Balls and Culture Secretary Andy Burnham sat on a pair of rope swings in a children's playground. The picture made it into most newspapers. Balls looks uncomfortable, squinting as the rope chafes his nether regions, Burnham, with good looks and a relaxed manner, pulls it off. Sometimes it is not what you do but the way that you do it.
Tara Hamilton-Miller was part of the press team at Conservative Campaign HQ from 2001 to 2006. She is now a political adviser.