Influential leaders from the Family Research Council and Focus on the Family publicly endorsed Rick Santorum for the GOP presidential nomination ahead of the South Carolina primary.

FRC President Tony Perkins and James Dobson, founder of Focus on the Family, announced their support Thursday. Both leaders said they were compelled to do so by Santorum's strong focus on social conservative issues.

"The institution of the family is the key issue facing this great nation. It is the foundation, the bedrock, upon which every dimension of Western Civilization rests," Dobson said in a statement.

He continued, "Of all the Republican candidates who are vying for the presidency, former Sen. Santorum is the one who has spoken passionately in every debate about this concern."

The endorsements are part of what has been a very good week for the former Pennsylvania senator.

On Thursday, the Iowa state Republican Party certified that Santorum, not Mitt Romney, was the winner of the state's GOP caucus. Earlier this week, Santorum also picked up the endorsements of Concerned Women for America leader Penny Nance and a council of evangelical leaders and Christian conservatives.

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Santorum's communications director, Hogan Gidley, said Wednesday that conservatives taking a renewed look at the candidates will find that the former senator is "a consistent conservative alternative" to supposed moderate Romney.

The Jan. 21 South Carolina primary is probably the biggest race for Santorum and the other GOP candidates. Historically, the winner of the South Carolina primary has gone on to win the Republican nomination.

State polls currently show that Newt Gingrich has risen to be the front-runner in the primary race. ABC News, however, aired an exclusive interview with Gingrich's second ex-wife, Marianne, Thursday night and it threatens to undermine the speaker's new lead.

Santorum, meanwhile, continues to trail behind Texas Congressman Ron Paul.