The LDS (Mormon) Church is the fourth-largest religious body in the US, claiming over 6.8 million members (about 1.7% to 2% of the adult population). It is significantly larger than minority US faiths like Jehovah’s Witnesses or Buddhism but smaller than the Catholic Church (~67M) and Southern Baptists (~13M).
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Losing 7 million Mormon voters, in addition to the lost Catholic votes, is not going to help the Trump Party in the coming up fast mid terms.