... Which makes me wonder where he got this idea from.
According to the AP:
But some readers have sent me this list of citations, which seem to back up the premise that some credible Mormon theologians, at least, believed that since God is the Father of all spirits, Jesus and Lucifer were brothers. Wikipedia seems to back it up, as well.The authoritative Encyclopedia of Mormonism, published in 1992, does not refer to Jesus and Satan as brothers. It speaks of Jesus as the son of God and of Satan as a fallen angel, which is a Biblical account.
A spokeswoman for the Church of Jesus Christ of Latter-day Saints said Huckabee's question is usually raised by those who wish to smear the Mormon faith rather than clarify doctrine.
I know virtually nothing about Mormon theology, but I think it is worth noting that Huckabee likely did not randomly pull this idea out of his head.
Regardless of whether or not this is a valid belief, it still seems apparent that Mike Huckabee would have been better served by not bringing it up in the first place.