Ohio voters are casting early ballots as Barack Obama struggles to thwart a John McCain victory in this crucial state.

The two candidates visit often while spending millions of dollars flooding television and radio with advertisements, mailboxes with literature and even voicemail with automated phone calls to get supporters to the polls, particularly during the current one-week window in which people can register and vote in one swoop well before the election.

On Monday, the State Supreme Court and two federal judges upheld a ruling by Secretary of State Jennifer Brunner that allows new voters to register and cast an absentee ballot on the same day during a period that began Tuesday and ends Monday. Republicans had opposed the policy, accusing Brunner of trying to benefit her fellow Democrats.

Most recent state polls show a dead heat; others give McCain a slight edge in Ohio, which holds 20 of the 538 votes in the Electoral College, the body that chooses the president. The last time Ohio supported a losing presidential candidate was in 1960, when it went for Richard Nixon.