A lot of Protestent Fundies really hate the LDS for purely religious reasons. LDS theology directly clashes with Traditional Christian thelogy big time.
Would not be surprised if this was a motive.
If only the shooter hadn't been "neutralized." Now people can speculate indefinitely what his motives must have been, and therefore what group to pin it on. It can't be just a nut with a gun anymore. That would send the message that guns aren't the problem. The nuttery has to be laid appropriately at the feet of whoever is then presumed to have radicalized him.
Officially, however, you'll see an outpouring of sympathy and support from other religions. Today they'll condemn the shooting (appropriately) and offer thoughts and prayers (appropriately) for the victims and survivors. Then next week they'll be back tweeting at each other with the renewed vitriol. The animosity goes both ways. Not only do Fundamentalists not care much for Mormons, but also Mormons (in large groups) tend to have a persecution complex. But that's not wholly directed at traditional Christians.
What is amusing is that a lot of Trump Fundie supporters are probably annoyed he refereed to the LDS as Christians, since they do not consider the LDS to be Chrisitan, but a bunch of heretics.
If holding a Bible upside down for a photo-op doesn't piss off the Fundamentalists, then I don't know what would. I'm not saying you're wrong. But I'm proposing that there might also be an amusingly tortured rhetorical gyration in this instance to let them continue thinking Donald Trump is their messiah but also that Mormons are still from the devil.
At age 101. Maybe the automatic election of the oldest to the officer of President/Prophet of the LDS is creating a lot of problems.
To be more accurate, the senior apostle almost always gets tapped. That's not necessarily the chronologically oldest person, but we're still quibbling over octogenarians. But it's according to the order in which they were appointed apostles, not how old they are. The heir presumptive is Dallin Oaks, a hard-liner on many of the social issues modern Mormons are facing. He's a former Utah Supreme Court justice. I read his book on the assassination of Joseph Smith,
Carthage Conspiracy; it was largely supported by the most recent biography of Smith written by a non-Mormon historian (
Joseph Smith: Rise and Fall of an American Prophet). We'll see how this turns out.