WASHINGTON -- The dustup over contraception underscored President Barack Obama's political edge in working to attract independent voters without alienating his Democratic base. His Republican rivals are forced to keep emphasizing their conservative credentials to attract the right-leaning activists who dominate the nominating contests.

It's a dynamic that usually plays out when a president seeks re-election without a primary challenger, and the other party fights to determine its nominee.

Obama already is in general-election mode, with the luxury of courting voters who don't ascribe to a political party. The eventual Republican nominee is moving to the right and probably will have to edge back toward the center in the fall. The farther he must go to the fringe to win the nod, however, the tougher his task.

The difference was clear Friday, at events two miles apart in Washington.

At the White House, Obama made a carefully calibrated concession to Catholics angered by his decision to require religious- affiliated employers, including Catholic hospitals and colleges, to cover birth control in their health insurance plans. The president tweaked the rule Friday. He said insurance companies would provide contraceptive benefits directly to employees, technically leaving employers out of the transaction.

White House and Obama campaign officials were relieved by the initial reaction.

Groups such as Planned Parenthood, which privately had urged no changes, praised the move. More important, so did the influential Catholic Health Association of the United States, whose criticism of the original rule spelled trouble for Obama's team.

At the same time across town, three of the four GOP presidential candidates appeared separately at the Conservative Political Action Conference, a major annual gathering of activists on the political right. Each tried to out-do the other in proclaiming conservative fealty.

Former Massachusetts Gov. Mitt Romney, former House speaker Newt Gingrich and former Pennsylvania Sen. Rick Santorum criticized Obama's contraception policy. They painted themselves as conservative crusaders on a range of issues.

Romney drew snickers by saying he was a "severely conservative governor." Gingrich said the Obama administration "is waging war on religion."

Santorum, who built much of his national profile by fighting legalized abortion, said Obama is "telling the Catholic Church that they are forced to pay for things that are against their basic tenets and teachings."

Democrats hope independent voters will see it differently. Americans, including Catholics, overwhelmingly embrace birth control. Obama's goal was to reframe his policy as a matter of equal access to preventive health care, not a quarrel about religious or economic rights.

"I think the president ended up looking like the responsible person in the room," said Lanae Erickson of the Democratic-leaning group Third Way, which has studied independent voting trends. "The Republican primary candidates went way out on a limb and will alienate themselves with independent voters," she said.