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Barry C. Burden, political science professor at the University of Wisconsin, said that if the trend from the nomination contests holds true, then Mr. Santorum “will not score well” in Wisconsin.

“In the 2008 Republican presidential primary, only 38 percent called themselves born-again or evangelical,” Mr. Burden said. “Perhaps that was partly a result of Huckabee not generating as much attention at that point in the race, but I would not suggest the percentage to be much higher this time around.”

Larry Sabato of the University of Virginia’s Center for Politics said that at this point in the race it is clear that the momentum has pivoted primarily on who votes — not the issues being espoused on the campaign trail.

“This has actually been a fairly easy contest to project,” Mr. Sabato said. “Single issues aren’t propelling the candidates; overall impressions among key constituencies in the GOP are. Mitt gets wealthy, college-educated, non-evangelicals including Catholics, and the Catholic Santorum gets middle-class, high school-educated evangelical Protestants. Gingrich also used to do well in Santorum’s base before this became a two-man race.”

The biggest pothole on Mr. Romney’s path to the nomination remains Texas, where Mr. Santorum is polling well ahead of the field. With a large evangelical voter population and the second highest number of delegates of any state, Texas hasn’t warmed to Mr. Romney - but Texas also awards its delegates proportionally, which will soften any blow Team Romney might be facing in the Lone Star State.

Many evangelicals in the states that have voted so far have questioned Mr. Romney’s commitment to their core issues. They particularly questioned his conversion from pro-choice to pro-life as governor of Massachusetts.

Those persistent suspicions were stoked again Wednesday when top aide Eric Fehnstrom told CNN that Mr. Romney could revamp his campaign after he wins the nomination.

“I think you hit a reset button for the fall campaign. Everything changes,” he said. “It’s almost like an Etch-A-Sketch. You can kind of shake it up and restart all over again.”

His opponents pounced. Both Mr. Gingrich and Mr. Santorum were captured in photos playing with Etch-A-Sketch toys, and the Democratic National Committee gleefully highlighted the story for reporters.