So, I was just talking about this to a friend. They said the same thing you did, but I disagree.
Now, I don't think making this post (but realizing he fucked up, and immediately deleting it) is a prosecutable crime. You're right, people are emotional and that factors into these things, generally.
However, I do think they'll investigate it. They'll at least have a chat with Chris.
The reason being, if a presidential candidate were to be assassinated, right around the election would be an extremely popular time period for someone to try, just because emotions are running high and everyone's freaking out.
And also, while there are millions of people out there blubbering about how triggered they are by Orange Hitler, the vast majority of them know better than to outright threaten to harm him. Some will, but most won't. There probably aren't as many threats as you'd initially guess.
So I think the Secret Service will pull in a bunch more people and do the legwork to check into as many threats as they can.
And as
@Ravenor and others have noted, this isn't unprecedented. They really will talk to you.