Strong opposition to the candidacy of Barack Obama in Arkansas may have helped conservatives pass a measure blocking the adoption of children by unmarried couples.

The measure, which voters overwhelmingly approved Tuesday and which prevents unmarried cohabitating couples from adopting or fostering children, won strong support from conservatives, exit polls found. The ban affects all unmarried couples but was written with the intent of preventing gay couples from raising children in Arkansas.

Unlike most states, Arkansas shifted to the right politically in this election. Senator John McCain won the state by 20 points compared with President Bush’s nine-point victory in 2004.

“I think white Arkansas Democrats felt cross-pressured in this race,” said Jay Barth, a political science professor at Hendrix College, in Conway, Ark. “They didn’t want to vote for what they viewed as Bush’s third term, but they also couldn’t bring themselves to vote for Barack Obama.