President Barack Obama's re-election team has asked a federal judge to reopen a target-rich window for all Ohioans to vote in person on the three days before Election Day.

In a federal lawsuit filed Tuesday, the Obama campaign, along with the Democratic National Committee and Ohio Democratic Party, argued that restrictions on balloting those days violate the U.S. Constitution's equal protection clause.

The suit, which names Secretary of State Jon Husted and Attorney General Mike DeWine as defendants, takes aim at the remnants of a Republican rewrite of state elections law. Facing a referendum fight, GOP legislators in Columbus repealed most of the measures in May but left intact a ban on in-person absentee voting during the final three days.

Many believe that stretch was key to Obama's turnout operation four years ago, when he won battleground Ohio by 4 percentage points. Democratic groups marshaled resources to bus voters to polling sites, and on the weekend before Election Day 2008, long lines snaked around the Board of Elections building in Democratic-dominated Cuyahoga County.

The Obama campaign cites research from voting rights advocate Norman Robbins, an emeritus neuroscience professor from Case Western Reserve University. Robbins estimates that 93,000 Ohioans voted in person on the Saturday, Sunday or Monday before Election Day 2008. But officials involved with the lawsuit denied the effort was politically motivated.

"Regardless of who votes on those final three days, it's a chilling notion that we should be opposed to those who vote in those final three days because they may not vote on our side," Ohio Democratic Party Chairman Chris Redfern said in a conference call set up by the Obama campaign. "I don't see any way that enforcing the right to vote is a political ploy."

Husted contended that Ohio's elections law must afford uniform ballot access across 88 counties.

"If consistency for voters is the premise that [Democrats] are after, then they should be very pleased with the changes that we made since I became secretary of state," Husted, a Republican elected to the office in 2010, said in a telephone interview Tuesday afternoon. "If their lawsuit were to be successful, that would not create equal access to voters that weekend before the election because in some counties the boards are open, and in some they are not."

But Democrats said the election rules exempt military personnel and others covered by the Uniformed and Overseas Citizens Absentee Voter Act from the three-day ban, allowing them more time to cast a ballot before Election Day. Those voters, according to the suit, can still vote in person at county boards of elections through the final Monday.

Don McTigue, an attorney advising Obama's campaign in Ohio, said this group was "arbitrarily" exempted. "What we believe is the deadline should be the same for everybody, and that would be the Monday before the election," he added.

Husted countered that the military exemption is a federal law.

"We don't have any ability to change that," he said.

The suit does not address a separate grievance from Democrats who are upset with Husted's decision last week to side with fellow Republicans and oppose evening and weekend hours for in-person absentee voting in Cuyahoga County.

Nearly 11,000 Cuyahoga County voters cast in-person ballots on the three days before Election Day 2008, according to the elections board. Obama beat McCain here by more than 258,000 votes. He won Ohio by about 262,000 votes.