COLLEGE STATION, Texas — Mitt Romney vowed Thursday that his Mormon religion would never interfere with his Oval Office duties, but after his much-anticipated speech there was no consensus on whether he'd halted his slide in key polls or erased doubts among Republican skeptics.

The former Massachusetts governor made his stance clear in a 20-minute address at the George H.W. Bush presidential library: "I will put no doctrine of any church above the plain duties of the office and the sovereign authority of the law. ... A president must serve only the common cause of the people of the United States."

Romney's challenge was that he had to accomplish three very different goals: disarm evangelical Christian Republicans' reservations about Mormonism, especially those in first-to-vote Iowa; essentially relaunch his stalled presidential campaign; and do both while also appealing to more secular voters, whom he'll need in contests to come.

"He's put himself in a box," said Dennis Goldford, a professor of politics at Drake University in Des Moines. "He's basing his campaign on the support of people for whom religion is of tremendous importance. But a lot of those people are suspicious of his religion."

It's difficult to say whether he won over evangelical Christians, who make up an estimated 40 percent of Iowa Republican caucus voters. They'll vote Jan. 3.

"Did he win over the evangelicals? Probably not," said Terry Madonna, director of the Center for Politics and Public Affairs at Franklin and Marshall College in Lancaster, Pa. "But he gave it his best shot."

Romney's task was similar to what John F. Kennedy did in September 1960, when he addressed questions about his Roman Catholic faith.

Just as Kennedy said he believed in an America where "no Catholic prelate would tell the president — should he be Catholic — how to act ... ," Romney told his audience, "Let me assure you that no authorities of my church, or of any other church for that matter, will ever exert influence on presidential decisions."

Romney, like Kennedy, offered not a lecture on the teachings of his faith but an affirmation of how his faith informs his judgment and his life.

Romney's speech was cloaked in symbolism. Former President Bush introduced him and said kind words about the Romney family, though he took care to note that he wasn't endorsing Romney or any other presidential candidate. And the address was given about 100 miles from the Rice Hotel in Houston, where Kennedy famously told Baptist ministers on Sept. 12, 1960, that he'd never take orders from the Vatican.

Romney referred to Kennedy's speech in his own.