New Jersey Gov. Chris Christie says he is backing Mitt Romney for president as "the man we need to lead America" and said attacks on his Mormon religion are "beneath the office of the president of the United States."

Christie announced his endorsement at a surprise appearance in New Hampshire with the former Massachusetts governor on Tuesday.

The event comes a few days after the Rev. Robert Jeffress, a supporter of Texas Gov. Rick Perry, called Romney's religion a "cult" and said he was "not a Christian." Jeffress was at an event where he introduced Perry.

On Tuesday, Christie said "any campaign that associates itself with that type of comment is beneath the office of the president of the United States."

Romney, for his part, called on Perry to "repudiate" the remark. A Perry spokesman said later that the call was an attempt to "change the subject," and noted that Perry has already disagreed with the comment.

Christie said last week that he would not be getting into the race for the Republican nomination, saying "now is not my time," but gave no indication an endorsement was coming soon.

A senior Romney adviser told NBC News that Romney secured the endorsement on Saturday when he and his wife, Ann, met with Christie and his wife, Mary Pat, at the Christie home.

Romney described Christie as an "American hero" who has battled to "rein in the excesses of government in New Jersey."

Christie's support -- which was considered to be coveted among the GOP field -- could come with his network of donors and admirers.

He has won national appeal among Republicans for being a brash, no-nonsense first-term governor who faced down the powerful teachers union and slashed the budget.

Perry's campaign said in a statement that he "has the utmost respect" for Christie "and looks forward to his help unseating President Obama next year."

Christie had repeatedly said he would not run for the White House, but had begun to waver in recent weeks. When he traveled outside New Jersey for several political appearances late last month, including a speech at the Ronald Reagan Presidential Foundation and Library, he said he began reconsidering his decision.

Ultimately, though, he reached the same conclusion he had felt for a long time.

"The deciding factor was -- it did not feel right to me in my gut to leave now, when the job here is not finished," he said last week.

For a complete timeline of Christie's journey, go here.

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