Senior Democrats voiced growing concern yesterday that the barrage of personal attacks against Barack Obama by his Republican rival are working and that he should hit back harder before it is too late.

Strategists on both sides of the political divide agreed that John McCain’s stream of negative advertisements, including one that compared Mr Obama to Britney Spears, have damaged the Democrat.

Since his world tour last month Mr Obama has been portrayed by the McCain camp as arrogant, presumptuous, addicted to celebrity and too elitist to connect with American voters. His lead in the polls has disappeared, and two surveys yesterday showed the candidates tied.

The attacks were orchestrated by the same Republican strategists who destroyed the White House ambitions of John Kerry in 2004. Their latest video, entitled The One, juxtaposes Mr Obama with images of Moses parting the Red Sea.

What has started to unnerve Democrats and aides to Mr Obama is that the narrative on news shows and among late-night comics has shifted, with attention focused on the inability of Mr Obama to surge ahead of Mr McCain in a year when the Republican brand is so toxic.

Many Democratic strategists are haunted by the fate of their previous candidates when confronted with Republican attacks, such as Mr Kerry, who failed to react quickly enough to the negative Vietnam Swift Boats campaign.

“Some Obama backers are right to worry that the relentless daily attacks on the candidate will take their toll on the campaign,” said Donna Brazile, the campaign manager for Al Gore in 2000. “It’s time for the Obama campaign to build a political firewall by using outside surrogates unaffiliated with the candidate to debunk these misleading attacks.”

David Gergen, who has advised Republican and Democrat presidents, said: “What we have learnt this week is that when the Republican attack machine cranks up, as Hillary Clinton predicted, [Obama] is actually pretty vulnerable.”

The tactics are risky for Mr McCain because they could alienate swing voters and leave the Republicans looking uninspiring. Strategists say that the explosion of race into the campaign poses dangers for Mr Obama at a time when he is trying to win over white blue-collar voters who refused to vote for him during his primary battle with Mrs Clinton.

After Mr Obama said that Mr McCain and Republicans were trying to scare voters by saying “he doesn’t look like all those other presidents on the dollar bill,” the McCain campaign accused him of playing the race card.

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