With senior Republicans openly expressing doubts about their early choice for the presidential nomination, Mr Bush had plenty to prove. And as he settled into his chair - this was the first debate without lecterns - he managed to combine a look of near-terror with a pose of almost arrogant slouch.
To be sure, he had heeded his critics - to an almost alarming degree. He tried to look engaged - none of the clock-watching or imperiousness of the first debate (or not much). He wore a broad-shouldered dark suit and a white shirt, the whole assemblage designed to project the seriousness that his critics said he lacked.
Gone was the half-smile, replaced by a semi-scowl that made him look more like the rottweiler Mayor of New York, Rudolph Giuliani.
Gone, too, were the vastchunks of campaign speeches that he had passed off as answers; these were replaced by considered pauses and references to his policies as Governor of Texas - relevant or not. He also trotted out some figures.
Occasionally, he set the standard. When asked which philosopher or thinker he most admired, he snapped back "Christ", in a tone that might have been an expletive coming from anyone but a southern governor before any audience other than Republicans in the farm state of Iowa. Asked by an almost disconcerted questioner to explain his reason, he twisted round in his chair and said in so many words that if you needed to ask the question you did not understand.
His reply floored his rivals, though, two of whom felt obliged to name Jesus Christ as their philosophical guide also.
Mostly, though, Mr Bush could only watch as his five seasoned rivals displayed their rhetorical skills to convincing effect. He was slower in his responses, less precise in his phrasing and diction, and sometimes almost lethargic. The brainpower question, as it is now known, was not answered.
Senator John McCain shone as has done before, and with far less to lose than Mr Bush. He decided early on not to campaign in Iowa, which holds the first presidential selection pro-cess, and is spending his money and energy in New Hampshire, where his image as outspoken maverick holds more attraction.
That strategy has paid off in poll numbers; he leads Mr Bush in that state.
Elsewhere, though, Mr Bush's lead is in double figures, and is diminishing only a little. The fear of the Republican establishment now is that they could be nominating a candidate who cannot win.
After yesterday's 90-minute session, prominent Bush supporters expressed relief. "I think the folks around the governor finally loosened up a little bit and let him be himself," said the Governor of Pennsylvania, Tom Ridge, who could be a candidate for vice-president on a Bush ticket.
Dennis Goldford, a professor of politics at Drake University in Des Moines, said: "I think Bush was a little more confident; he didn't have that deer- in-the-headlights look. But his campaign is still a folksy, common-sense affair rather than a hardened policy-wonk sort of thing. McCain was much more substantive."
If anything, though, Mr Bush seemed to impress the pundits more than the voting public of Iowa, many of whom would not have seen the first two debates in which Mr Bush took part. One audience survey found that support for Mr Bush in their sample dropped by almost one-third between the start and the finish of the debate - not something the Bush camp would be happy to hear.Reuse content