The Nick Clegg bandwagon has not been stopped. This was the most significant point to emerge from the debate. There was not a single moment or sequence when a viewer would have sensed that politics was returning to "normal", or at least to what it was before the first debate. This was David Cameron's challenge, admittedly a daunting one and perhaps an impossible task. Somehow or other he needed to create a sense that we have all been living in a mad fantasy world for the last seven days and of course the Conservatives were marching to an overall majority and the Liberal Democrats were a bunch of amateurish, divided opportunists.

Cameron was pretty good and for someone who has enjoyed a very generous media on the whole is being unfairly criticised in some quarters for his performances in the debates. He was not bad last week either. In particular last night he was wise not to make too many presentational or strategic changes. There were more echoes with last week than frenzied departures and that was sensible. But he did not get anywhere near changing the current extraordinary situation.

Clegg held his own throughout and in some ways gave a more thoughtful performance than last week when his anti-politics stance and his distancing from both Brown and Cameron were shameless and entirely successful. He had some obvious cards, not least his party's opposition to the war in Iraq. But when the two other leaders ganged up on him over Trident he was not remotely troubled.

Novelty becomes familiar very quickly. Last week's debate felt surprisingly fresh and significant. Within minutes of the end the exchanges became explosive and perhaps historic when Clegg was hailed as the triumphant winner, a victory that fed on itself. Yesterday's event, although more lively and sparky, did not take off in the same way. Perhaps the only revelation of the campaign came and went like an electric shock in Debate One, that Clegg could hold his own with the big two. Inevitably the impact the second time around was less dramatic.

That was partly because both Gordon Brown and Cameron raised their game, in terms of projection and substance. Stylistically Cameron looked very consciously into the camera and the television audience rather than those gathered in the studio, a mistake he made the first time around. Brown was more passionate, aware that solidity alone cannot prevail in an election where the stakes are suddenly even higher than they were before. Both addressed Clegg and his policies more directly.

Over the renewal of Trident, Cameron delivered the best joke of the evening when he noted: "I agree with Gordon." It was more than a joke. He sought to imply that the leader that has come to personify change represented in reality a threat. Brown did not repeat his defining phrase from the opening encounter in which he declared several times: "I agree with Nick." Now that Nick and his party has leapt over Labour there was much less cause for agreement. "Get real, Nick," was his less solicitous declaration.

Beyond the inevitable onslaughts on the soaring Clegg the dynamics of the second debate were the same as the first. Brown played the world statesman. The buck stops here, he declared at the end, in an attempt to convey strong hard-headed leadership. Still his delivery was too close to his performances in the Commons than is appropriate for this format. Cameron's overall theme was the one that he knows he must reclaim as a matter of urgency, that he is the agent of change. At times he appeared to be genuinely angry about Labour's leaflets claiming the Conservatives planned to take benefits away from pensioners.

At one point Brown tried to make a joke about the others squabbling like kids. It was not well delivered and too obviously pre-arranged. More importantly that was not how it seemed. Both were debating intelligently. Brown is still the least comfortable with the format and cannot spend another week admitting he lost on style but that "it's all about substance". Communicating the substance is the key and while Brown had the strongest arguments in some sections, especially the early one on Europe, he was too dependent on phrases uttered many times before. He is always authoritative, but let us remember he needs a game changer almost as much as Cameron. He did not get one last night.

Quickly the focus will move on to next week's final debate on the economy. I cannot quite see how Clegg becomes significantly diminished on that theme. Perhaps other factors will come into play before polling day, but as far as these debates are concerned a pattern is in place. Clegg was given a rare opportunity. He has taken it.