It is the Mormon religion that first attacked Christ and His followers by making many false claims about Him, including that He is the Devil’s brother: Jesus was the spirit brother of Lucifer - according to this doctrine Jesus became the Savior because he came up with a better plan than Lucifer concerning how to get the people on earth to worship God (see Pearl of Great Price, Book of Moses, 4:1-3).
Romney defends the religion that teaches this false gospel.
Mormons do believe that Christ had a better plan than Lucifer but it was not Christ’s plan, it was God’s plan, Christ was simply following it.
According to LDS doctrine, Jesus and Lucifer were no more brothers than you and I. This is a blatant misrepresentation of our beliefs by those who would paint us in a bad light.