…The readers' letters are being sent only to voters flagged as "undeclared" in the county's electoral roll, a public document the newspaper bought from local officials, then placed on the internet.
The Guardian says it chose Clark County not just because winning Ohio is vital to Mr Bush's hopes of victory, but because the rolls showed such a large number of undeclared voters - 54,000 not affiliated with either party.
But the newspaper misunderstood Ohio polling law, according to the county's elections supervisor, Linda Rosicka. Being "undeclared" on the roll means someone did not choose to vote in the last two party primaries, in which party candidates are chosen. "It doesn't have anything to do with being undecided," she said.
Many local Democrats expressed sympathy with the desire of British voters to have a say. That does not mean they are happy the letters are coming...
Across America, the Guardian project has sparked disdain from the Right, and dismay from Kerry campaigners. Coverage in the US media has stressed the risks of offending voters. Furious e-mails have reached the Guardian, such as this one from Texas, stating: "Real Americans aren't interested in your pansy-ass, tea-sipping opinions."
In Clark County, Mr Harkins, the local Republican chairman, has no doubt that the Guardian has helped him - and Mr Bush.
He showed figures from Republican polls, indicating that only four per cent of the county's voters were still undecided last week.
"This is a very competitive county, where the undecided vote is very small. What the Guardian has done is firm up the Republican base. What a gift."