The Supreme Court on Tuesday cleared the way for voters in the battleground state of Ohio to cast ballots on the three days before Election Day, giving Democrats and President Barack Obama's campaign a victory three weeks before the election.

The court refused a request by the state's Republican elections chief and attorney general to get involved in a battle over early voting.

Ohio is among 34 states, plus the District of Columbia, where people can vote early without giving any reason. About 30 percent of the swing state's total vote — or roughly 1.7 million ballots — came in before Election Day in 2008. Crucial to Obama's win that year was early voting in Ohio, North Carolina and Florida.

Obama won Ohio four years ago, but Republican rival Mitt Romney is making a strong play for it this year. No GOP candidate has won the White House without Ohio in his column.

Obama's campaign and Ohio Democrats had sued state officials over changes in state law that took away the three days of voting for most people but made exceptions for military personnel and Ohioans living overseas.

Their lawsuit cited a recent study saying nearly 105,000 people voted in the three days before the election in 2008, and they argued everyone should have the chance to vote on those days. They also said eliminating the opportunity for most Ohio residents to vote in person on those days, while giving military or overseas voters the chance to do so, leads to unequal treatment.