Jonathan Packman has spent the past few days enjoying poolside views of the Atlantic at his elderly Jewish grandparents' condominium, eating quantities of their Mandel Bread – while trying to ensure that “pop pop” and “mom mom” vote for Barack Obama.

“I think my grandmother is moving towards Obama,” he says. “My grandfather is still undecided. He is old-fashioned and is having a hard time getting his mind wrapped around voting for a black man.”

Mr Packman has travelled from the ultra-liberal city of Berkeley, California, hoping that he can use his influence as a grandson to flip Florida – and the White House – back into Democratic hands.

It is called “The Great Schlep”, an effort organised by the pro-Obama Jewish Council for Education and Research, which should lead to hundreds of grandchildren descending on the Fort Lauderdale area for the Columbus Day weekend to combine an annual family visit with some ruthless political activism.

The reason is that elderly Floridean Jews, most of whom have migrated south for some retirement sunshine, are potentially the key swing voters in this crucial swing state.

They make up about 5 per cent of the state population but in Fort Lauderdale and Palm Beach County – where the shenanigans over hanging chads and uncounted ballots eight years ago gave the world President Bush – they number as many as one in four voters.

Although the latest polls in Florida suggest that Mr Obama is narrowly ahead, he has a problem with this usually reliably Democratic demographic. One survey suggests that he is supported by 57 per cent of Jews – compared with the 77 per cent for John Kerry four years ago.

Some believe that this reflects a long-term trend among Jewish voters, especially those driven by family values and national security, towards the Republicans. Others suspect that his race and a possibly undeserved reputation for having Arabist sympathies are significant factors.

Outside the Young Israel Orthodox Synagogue in Hollywood, near Fort Lauderdale, there is clear evidence of hostility to him. Marc Hammerman, a 57-year-old doctor, who voted for John Kerry in 2004, says: “I just don't believe Obama on Israel. I don't trust him. He vacillates.”

Robert Aschheim, a lawyer, says: “I switched to the Republicans after 9/11. I'm a Jew. Security is important because we've had 2,000 years of insecurity. My kid is pretty liberal – but what the hell, he's 24 years old. I'm trying to change him.”

Howard Rotterdam, a retired teacher, is sticking with the Democrats even though Mr Obama was not his preferred choice and admits that “a lot of people here are afraid of him”.

Raananah Katz, an ophthalmologist and McCain supporter, says: “Obama is someone who did not excel at high school or his first university but goes to Harvard Law School? My son is there and I know how much he went through to achieve that. Maybe doors opened for him or maybe he is gifted? I don't know.” Who will her son vote for? “Haa!” she replies. “I don't even ask.”

Mitt Weiss, 82, and his wife, Arlene, 65, are Republican for the first time in their lives. “Obama is soft,” Mr Weiss says. “He wants to talk to the Iranians, which is insane.”

His nephew, Joel Barron, 39, visiting from Los Angeles, says: “I'm putting some pressure on them to vote for Obama – but clearly not enough. There are some pretty intense conversations going on around the dinner table. I think there is a touch of racism in all of this.”

David Ogman, a 32-year-old stockbroker, has had better luck with his grandmother in Palm Beach.

“I made a list of pros and cons for her on paper and once she saw Obama's views on Medicare, social security, foreign policy, she was able to look beyond his name and the colour of his skin.” He predicted that Connie Greenberg, 72, who left for a Caribbean cruise this week, will “definitely vote the right way”.

Mr Ogman dismissed suggestions that there was bad blood between the Jewish and black communities. “It's just about age. Retirees like we have here in Florida have an old-school mentality and are used to voting for the white guy.”

Great Schleppers arriving in Fort Lauderdale, where the high-rise retirement condominiums jostle for space all the way down the coast, have been provided with fact sheets headed by phrases such as “He's black – let's talk about it!”. These provide details of Mr Obama's support for Israel, point out that he has run the “business side of his campaign better than any other candidate” and claim that he is different from previous, more confrontational, generations of African-American leaders.

In an accompanying video, the Jewish comedian Sarah Silverman makes the case in her own fashion. “Explain to them that we're all the same inside.

“You know, you could compare an elderly Jewish woman like Nana to a young black man. They may seem totally different but on paper they're the same,” she says. “I mean, think about it, tracksuits! Let's start there. They both love tracksuits! They can't get enough of them. What else? Car choice – the Cadillac!

“They're both crazy about their grandkids. What else? They like things and bling and money and jewellery and stuff. They both say ‘yo' all the time. Or Jews go right to left – 'Oy'. Uh, what else? All their friends are dying.”

She adds: “You don't have to use facts. Use threats. If they vote for Barack Obama, they're gonna get another visit this year. There's nobody more important or influential over your grandparents than their grandkids – you! If not, well, let's just hope they stay healthy until next year.”

Mr Packman, a 40-year-old financial analyst with the Whole Foods grocery chain, says: “I could never withhold visits to my grandparents. I will come back no matter what. But I'm visiting with my son and I want them to know how important this election is to his generation. I've spent a lot of time sitting around the pool, talking politics with all their friends – my grandparents are still very vivacious people.

“I stress that Obama is focused on integrity. He's a very dignified guy while McCain has been stooping to a low level.”

His grandparents Bertha and Julius, both 91, declared yesterday that they would vote for Mr Obama. Mrs Packman said: “Jonathan, he's been using all the tactics on us but he doesn't have to try too hard. We've moved down from New York to live the life a little and I really don't like Republicans.”

She added: “I just want to say how nice it's been to have our family visit us.”

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