To be honest, the idea anybody is safe these days is rubbish. You could kill pretty much anybody you fancied... the thing is that the rules are different, take for example the IRA, despite there being plenty of casualties during the "troubles" their bombing campaign was always about dirsuption and importantly people were not necessarily willing to die for the cause (at least not needlessly). This made both detection and stopping such activity easier, but today with people willing to get caught up in such things there isn't really any stopping them.
In most cases body guards are there to stop something like a kidnap, look at the success rate of presidencial assasinations, pretty high to be honest.