@JasonPerseus I have to imagine that attempts that are thwarted by the Secret Service far earlier in their inception/execution are more common. This is just one that got through the net.
@JasonPerseus True, but from what I understand, they swarm those rallies and their presence is ubiquitous. You don't have to lock down the whole country, just a couple square blocks.
This guy talks about it in this video: https://www.youtube.com/watch?v=Q-fSDCb_JEc
He talks about how there were soo many Secret Service agents everywhere that the idea of an assassination attempt didn't even cross his mind until long after the shooting.