There are two (three?) different sorts of threat. Broadly speaking, the domestic crazy and the international terrorist. Historically Door #1 has been the big one. Nowadays there’s increasing interest in Door #2 as one of the ultimate examples of asymmetrical warfare if they can pull it off.
My software firm made various tools for homeland security and public safety. One of which was an intel fusion system for tracking info tidbits and their potential connections. Which we ended up selling to several personal protection companies. Along the way we learned a lot about a shadowy world I’d never known of.
Darn near any celebrity whose name you’d recognize has a collection of crazies that are obsessed with them. “Celebrity” can be an athlete, an entertainer, a politician, a big businessman, etc. As an example who’s now safe to talk about, Steve Jobs would fit this description. I’m not implying he or his family was or is a customer; he’s just a short recognizable name that’s easy to type.
During his life, somebody like Jobs probably received 50 letters, faxes, or emails *every single day *from crazies. A bunch are one-offs, but the others are repetitive, sending messages weekly, daily, or more often. Some asking for money, others wanting to have sex, and others discussing, ad nauseum, the long relationship they’ve had with Jobs and their plans for the future. Folks with well-known spouses and kids find their whole family gets similar treatment from the wackos.
Most of these nuts most of the time live on disability and little else far from where the celebrity lives & works. And hence pose(d) little real threat. Some of them, OTOH, had real jobs, families, incomes, credit cards and all the rest. And could potentially show up any day at any place in the country where their celebrity happened to be.
So somebody has to collect, evaluate, and curate all this stuff. Crazy is inherently unstable over time. Folks get worse or better or wander off to develop a different obsession. But some of them slowly work themselves into a crescendo of agitation and anger and hate. At which point the private security folks start involving the public authorities, perhaps even physically watching the subject to ensure they don’t travel unnoticed to someplace the bigwig will be.
Every trip by the celebrity to anywhere includes checking the database for known threats within a couple day’s drive. And considering whether those semi-locals are worth taking extra countermeasures for this time.
This is all for somebody like Jobs or, say, Bono. I.e. somebody who doesn’t have an entire industry devoted to inciting hatred at them. Unlike the President.
I have to imagine the volume of crazy aimed at hating Obama (or soon Trump) is mind-boggling. Understand also this is only the crazies who bother to write. There are plenty more who don’t. Plus the more serious plotters that may be out there. In the case of Presidents you’ve got sovereign citizens, survivalists, and all the rest.
I had always considered “bodyguards” to be affectations, a form of conspicuous consumption by showy people with show-offy personalities. I think there’s certainly still an element of that for some Hollywood types. But I now understand there’s a lot more steak behind the sizzle.
The relative ease of getting firearms and explosives in this country certainly helps anyone who wants to take action to do so. e.g. In the UK gun control doesn’t slow down the IRA very much, but it does slow down some nutter from the countryside or living in grim public housing. In the US, not so much.