Huntsman, the former Utah governor, has already said he does not plan to sign the pledge, which has the backing of more than 150 tea party and conservative groups. A dozen Republican senators and 20 House members are also on board.
One of those senators, South Carolina's Jim DeMint, told CNN over the weekend that the pledge is a litmus test for his support said he has ruled out backing Huntsman's bid as a result.
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