The western state of Colorado has become a focal point in this year's presidential race, as it considers an amendment that would split its nine electoral votes in proportion with the popular vote.
If approved by voters, Amendment 36 would come into effect immediately and apply to the November election.
Analysts say the measure could be the deciding factor in an extremely tight race.
Opinion polls indicate if the election were held in Colorado today, Mr. Bush, who holds a slight lead in opinion polls, would earn five electoral votes and Mr. Kerry would earn four. Analysts say if the system had been in place in 2000, Al Gore would now be president.
The measure has supporters and opponents in both parties, though some Republicans have denounced the amendment as an effort to manipulate the election.
Supporters say abandoning the winner-take-all system increases the importance of each individual's vote.
Maine and Nebraska are the only two states that currently split their electoral votes.