On one side, 15 states have joined Ohio in asking the Supreme Court for emergency protection from federal judges who seek to “micromanage” elections.

On the other, President Obama’s reelection committee has invoked the lessons of Bush v. Gore to counter that Ohio is attempting to favor one group of voters above all others.

And now, in a case with legal and political ramifications, the Supreme Court must decide whether to intervene just three weeks before the election in a state that both Obama and Republican challenger Mitt Romney consider critical to their chances of winning.

The issue is whether Ohio may allow only military voters to take advantage of in-person early voting in the three days before the Nov. 6 election. A district judge and a panel of the U.S. Court of Appeals for the 6th Circuit said the state had not shown why it should differentiate among groups of voters.

“While there is a compelling reason to provide more opportunities for military voters to cast their ballots, there is no corresponding satisfactory reason to prevent nonmilitary voters from casting their ballots as well,” the appeals court said. About 105,000 voters had cast their ballots during the three days in question in 2008.

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Ohio’s request that the Supreme Court stay the appeals court decision comes amid an unprecedented number of voting law changes across the country, concerning who is eligible to vote, under what circumstances and how those votes will be counted.

It has led to fierce partisan battles and a string of lawsuits that mostly have been concluded without the high court’s intervention. But Ohio wants the justices to set aside the 6th Circuit’s ruling and allow its changes to go into effect.

Although the state has permitted early voting on the weekend before the election in the past — long lines on Election Day in 2004 prompted the change — the Republican-controlled legislature ended weekend voting this year, saying local boards of election needed the time to prepare. The state made an exception for military voters, who it said could be deployed at any time and thus miss the chance to vote.

Such decisions, Ohio says, are for each state to make. The 15 states supporting that position — all, like Ohio, have Republican attorneys general — told the court that the Constitution’s “genius” is to allow states “to consider and implement creative, novel efforts to widen the ability of citizens to vote.”

But Ohio Democrats complain that plan is partisan, saying the voters most likely to take advantage of voting on the weekend before the election are women, the poor and older voters. The Obama campaign told the justices that the lower courts were right to stop Ohio’s plan.

Bob Bauer, the general counsel for Obama for America, wrote in his brief that the system “is as arbitrary as it is unique: nowhere else in the country will an eligible voter be turned away from a single, open polling place because the polling place is open for some voters, but not for that particular voter.”

The lower courts’ rulings relied in part on Bush v. Gore, the Supreme Court’s 2000 ruling that stopped the Florida recount in the presidential race between George W. Bush and Al Gore. The justices have not relied on that ruling in any case since.

But judges in the 6th Circuit have cited the decision’s command that “having once granted the right to vote on equal terms, the state may not, by later arbitrary and disparate treatment, value one person’s vote over that of another.”

The motion before the court is not on the merits of the 6th Circuit’s decision but on Ohio’s request that it be stayed. The state says it already provides 23 days of early voting — which began Oct. 2 — and makes it easy for voters to cast their ballots by mail.

But the Obama campaign said the state cannot show any irreparable harm to opening the polls to all voters that weekend. It points out that the lower court’s decision simply restores the status quo from the 2008 and 2010 elections, and it notes that several large counties have said the extra voting helps alleviate problems from large turnout on Election Day.

Besides, the brief notes, any hardship on the state “is far outweighed by the harm to voters who are arbitrarily denied the right to vote on the same terms as their fellow citizens.”

A decision on whether to grant the stay could come anytime. Ohio’s plea was sent to Justice Elena Kagan, who is assigned to the 6th Circuit, and she called for the response from the Obama campaign.

Kagan could rule on her own, but in such cases the designated justice usually refers the matter to the entire court.