Exit polls indicated that Louisiana's primary saw a high turnout of voters who identified as very conservative — a group that has typically favored Santorum. Also helping Santorum was a high turnout of religious voters — nearly two-thirds of voters in today's primary said that they go to church at least once a week.
Santorum is Romney's chief challenger and a former Pennsylvania senator who has won previous contests in Tennessee, Mississippi and Alabama.
A Louisiana victory is unlikely to change the overall dynamics of the race. Santorum still dramatically lags Romney -- the former Massachusetts governor -- in the hunt for delegate to the GOP's summertime nominating convention. Former House Speaker Newt Gingrich of Georgia was far behind in the Louisiana vote count.
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The Associated Press contributed to this report