The Bill and Hillary show rolls into town, promising to leave the limelight to Kerry

Amid massive security and huge expectations from those wishing to oust President George Bush from the White House, the Democratic National Convention opened yesterday in Boston with a demand for the party to "stay positive".

Amid massive security and huge expectations from those wishing to oust President George Bush from the White House, the Democratic National Convention opened yesterday in Boston with a demand for the party to "stay positive".

Former president Bill Clinton, his wife, Senator Hillary Clinton, former president Jimmy Carter and Al Gore, whose bid for the presidency failed four years ago, last night opened the week-long convention. The opening night's speakers were selected to remind the party not only of its previous successes but of its failures, and of the need to unite against Mr Bush.

Yet with polls showing Democrats and Republicans neck and neck across the country, the party's presidential candidate John Kerry and Democratic officials have told delegates they must refrain from excessive criticism of the President for fear of alienating swing voters, tired of negative attacks. "People live the negatives in their lives all day," Mark Mellman, a Democratic pollster, told reporters. "What they need to know is more about John Kerry."

Despite all the talk of positive messages, Mr Kerry stepped up the rhetoric against Mr Bush last night, saying: "Never in 35 years have I seen the United States as much the target, much sort of derided and as disrespected as we are today, where Americans when they travel abroad are at risk."

Mr Kerry's first hurdle will be to rise above the spectre of Mr Clinton, whose spark and campaigning skills he so clearly lacks. In an attempt, perhaps, to deflect attention Mr Clinton was staying not in the city proper but in the suburb of Cambridge and he promised that he would not loiter after giving his speech.

"The President may still be re-elected, because he's a great politician, but if he's not, it will be because of the response that he decided to undertake after 9/11," Mr Clinton told the Los Angeles Times. "A slight majority seem to have decided that they would like a new president. Kerry just has to close the deal."

Mr Clinton, who is staying at the Charles Hotel, along with the actors and Democratic supporters Danny Glover and Ben Affleck, added: "I feel good about the way [Mr Kerry] relates to voters ... I'm going to give a talk and get out of town."

Mrs Clinton, whose own ambitions for the White House have been complicated by the selection of the youthful John Edwards as Mr Kerry's running-mate, was also due to address the convention and introduce her husband. Mrs Clinton, a senator for New York, told CNN: "I am so excited about replacing this administration. The Bush-Cheney presidency has been bad for America and bad for the world. I cannot wait to see them leave the White House, the sooner the better. I wish we could move the inauguration up a few months."

Apart from the somewhat awkward presence of the Clintons, the challenge for Mr Kerry and the Democrats this week has been made clear by two recent polls, one of which showed more than 90 per cent of registered voters had already made up their minds about who they wanted to support and another which showed a third of voters felt they still did not know enough about Mr Kerry.

Surveys suggest that the small tranche of undecided voters who will determine the outcome of November's election is more moderate than many Democrats and likely to be won over by a more positive message rather than a campaign of continuous Bush-bashing. In terms of policy, it is unlikely that the convention will provide anything particularly unpalatable to those "undecideds".

In terms of raising Mr Kerry's profile, senior Democrat figures have stressed the need to concentrate on his leadership qualities, experience and "character". The Rev David Alston, who was a member of Mr Kerry's boat crew during the Vietnam War, was also due to address the convention last night with his testimony of the candidate's leadership strengths.

The convention chairman, Bill Richardson, the Democratic governor of New Mexico, said: "Our objective is to show the personal side of Senator Kerry ­ his character, his Vietnam service, his leadership qualities. The reality is that the American people don't focus on who they are going to vote for entirely until the conventions period. What you want to do is draw them in with a message of what we're going to do."

Mr Kerry, who threw the opening pitch at a baseball game between the Boston Red Sox and the New York Yankees on Sunday night, has been campaigning in the key swing state of Florida where he stressed the need for affordable health care. He is due to make a grand entrance to the convention on Thursday before his formal acceptance of the nomination and his speech to delegates.