How was it for you? Did the earth move for you in Denver? If you'd asked delegates to the Democratic convention these questions on Thursday evening after Barack Obama's speech accepting nomination as his party's candidate for the presidency of the United States, you would have got enthusiastic and affirmative answers.

Four days before, the convention opened in an atmosphere of some nervousness. There were hurdles to be crossed every evening: on Monday with Michelle Obama, the candidate's wife; on Tuesday with Hillary Clinton; and on Wednesday with Bill Clinton. All three of them passed the test. The sighs of relief in the convention hall were audible. The Democrats don't do nuance. Only full frontal will do, and one by one all three did what the convention required.

And on Thursday night Obama gave the aggressive speech of a candidate already in transition from primary to presidency. There were passages of coruscating oratory. There was detail on tax, energy and defence. The fireworks were brilliant, the choreography precise. The supporting speakers were unflinchingly on-message.

Job done, then? Yes and no. The Clintons, for all their protests to the contrary, remain out of sorts. How they are deployed during the presidential campaign will require judgement and sensitivity. Hillary's women are not all reconciled to her failure to win the nomination.

Once the euphoria of Obama's reception died down, there were seasoned commentators who were comparing his speech not entirely favourably with Bill Clinton's more restrained brilliance of the night before. The issues that were raised in the primaries about Obama's experience and judgement remain. Twenty-one former generals and admirals were paraded on the podium before he spoke to testify to his readiness to assume the responsibilities of Commander in Chief. But the fact it was necessary to muster such top brass at all shows that on this issue the Democrat high command is still nervous.

There were too some hostages to fortune. A commitment to end dependence on Middle East oil in 10 years was both ambiguous and ambitious. Some promises on the economy were specific but the challenge of globalisation was never mentioned, nor was the protectionism that seems to underpin the candidate's thinking made explicit. How the speech will go down outside the confines of the faithful is yet to be seen. Wiser commentators say never judge the impact of the Democratic convention until the Republicans have held theirs. Remember that Michael Dukakis, Democratic nominee in 1988, left the Atlanta convention 17 points ahead of George Bush Snr but still lost.

But throughout the past few days the marvel has been not policy or personality but the fact that a black candidate could now be nominated to contest the highest public office in the US. You had only to look round to see that in the Democratic party at least there is opportunity, equality and integration. Black and white do not only respect each other; they are at ease with each other. Jesse Jackson Jnr, a member of the House of Representatives, looks and sounds like the chief executive of a major corporation. Unlike his father he does not need to rail against the party, he is accepted for himself . It is a far cry from the bitterness of the past.

And it is also a far cry from the triumphs of the past. Teddy Kennedy, the last of the three brothers, left his hospital bed to come to Denver, his treatment for cancer put aside, so that he could give Barack Obama the support of the Kennedy legacy. His illness has clearly taken its toll but in his speech there were still occasional flashes of the Kennedy family brilliance. The Harvard vowels were evocative of another time and place. And he finished with clarion of his speech in the 1980 convention in New York when he withdrew his challenge to sitting President Jimmy Carter for the nomination. "The dream lives on" may still excite the faithful but it is from another political age.

Obama talks of change but there is more than a suspicion that the change he advocates sounds like a reversion to some golden age. The twin ambitions are said to be the rebuilding of the American dream, of which he is a conspicuously successful example, and the restoration of respect for America abroad, badly damaged by the adventurism in Iraq. He wants to restore respect for the Constitution and to close Guantanamo. He wants to end the war in Iraq "responsibly". These seem less like change and more like a return to a benevolent status quo.

Change is indeed a regular theme in democracies. Merkel in Germany, Sarkozy in France, even early Blair and Brown in Britain. But real change involves risk. In the presidential election, change in the US appears to centre not on what Obama would do but the fact that he would be doing it. If Bush's eight years had not been so troubled would Obama still have had appeal? And is there a lesson for us in the United Kingdom? When inconveniently canvassed, the British electorate will take refuge in "it's time for a change", but does that mean a change of direction or a change of leadership?

As Denver showed, sentiment is ever present in American politics. No speech is complete without fulsome tribute to parents, no appearance complete without the accompaniment of scrubbed children and a wholesome wife. Emotions which in Britain are regarded as too private to be shared are unashamedly laid bare publicly. The British electorate is more reserved and less easily moved. When politicians talk about change in Britain the voter wants to be able to measure it, not just to feel it. Denver excites the heart but Birmingham, Manchester and Eastbourne, when all three parties meet this month, will be much more about the head.

The writer was leader of the Liberal Democrats 2006-7

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