Democrats and Republicans are making an unprecedented effort to register and court United States voters living overseas in the belief they could provide the crucial boost to secure the upcoming election.
With polls showing the two candidates neck and neck and with less than six weeks before polling day, the parties are stepping up efforts to gain the support of an estimated three million eligible Americans voters living outside of the US.
More than half a million of them live in Mexico and in the town of San Miguel de Allende, consular officials have twice had to order more application forms to meet the demand.
As a sign of the importance the parties attach to this expatriate vote, President George Bush's nephew, George Prescott Bush, spent four days in Mexico last month campaigning for his uncle. At the same time, Democrats living in Mexico received a rallying visit from John Kerry's sister, Diana. Both parties have established well-organised groups to co-ordinate voters, not just in Mexico but in scores of countries.
"I do think there is an unprecedented effort being made by the parties," said Curtis Gans, the director of the Washington-based Committee for the Study of the American Electorate. "Whether it is because of the closeness of the race, I am not sure. People want to get out the vote but I also think it is because of the lightning rod that the Bush presidency represents. People feel so strongly that they want to leave no stone unturned. This is probably the most emotional election in my lifetime and I'm 67." While there are no official records of who these expatriate voters support, it has always been assumed that absentee ballots from overseas were predominantly in support of Republicans, given the high number of military personnel and retirees.
But Democrats believe that this time around the Republicans may not hold the advantage. They argue that because of the international opposition to the war in Iraq it will be easier to attract votes in support of Senator Kerry.
Ana Maria Salazar, a dual US-Mexican citizen and former White House official who served under President Bill Clinton, is the Kerry campaign's co-ordinator in Mexico. She told The Chicago Tribune: "We're so convinced that these people are going to vote for Kerry. These are probably the people who most feel the impact of President Bush's foreign policy mistakes."
Larry Rubin, a Mexican-born businessman who is in charge of the Republican effort, said they had not always been very organised but this year his group was receiving support from Republicans Abroad, a group that co-ordinates overseas support overseas for candidates from the party.
Mr Rubin said he believed that most overseas voters would support President Bush, arguing that most voters in Mexico were concerned with economic issues such as the outsourcing of US jobs and tax rules for citizens abroad.
It is impossible to know the effect the overseas voters will have. Their votes will be counted in the state they list as their "permanent residence". If this is one of the dozen or more battleground states where in 2000 just a few hundred votes separated Mr Bush and the Democratic candidate, Al Gore, such votes could be crucial. "They could be crucial if they are registered in a swing state. But if their vote is counted in [heavily Democratic] New York and [heavily Republican] Utah, it will make no difference," said Mr Gans. Because of the wish to have better information about the numbers of overseas voters, under new provisions passed after 2000, the federal Election Assistance Commission must start counting absentee ballot applications and actual absentee votes cast.