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A prominent Christian leader said Thursday that "my conscience and my moral convictions" prevent him from voting for Rudy Giuliani should he win the Republican nomination.

In a blistering online column, Focus on the Family founder James Dobson wrote that, should the former New York mayor become the nominee, "I will either cast my ballot for an also-ran — or if worse comes to worst — not vote in a presidential election for the first time in my adult life."

"Many liberal Americans will agree with the social positions espoused by Giuliani. However, I don't believe conservative voters whose support he seeks will be impressed," Dobson said on WorldNetDaily, a conservative news Web site.

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A Christian evangelical based in Colorado Springs, Colo., Dobson said he was speaking as a private citizen. However, his words carry considerable weight with the some 7 million listeners of his conservative radio show.

Earlier this year, Dobson said he won't back John McCain because of the Arizona senator's opposition to a constitutional amendment banning same-sex marriage. Dobson has given no public indication on how he feels about the other top-tier candidate, former Massachusetts Gov. Mitt Romney. The two, however, have met privately.

Dobson called Giuliani an "unapologetic supporter of abortion on demand" and criticized him for signing a bill in 1997 creating domestic-partnership benefits in New York City.

He said there were other "moral concerns" with Giuliani, including that he's on his third marriage to "his mistress" from his second marriage and "appears not to have remorse for cheating on his wife."

Last week in a speech in Houston, Giuliani urged Republican voters to look beyond the differences they have with him on social issues and said it was important to respect those with whom one disagrees.

"From the beginning Mayor Giuliani has been straightforward with the American people about where he stands on the issues," said Maria Comella, a Giuliani spokeswoman. "It is a sign of leadership to speak honestly about your beliefs even when it is not politically expedient."

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