Also, thinking about this further, in "statistically normal times" I would agree more with Dogmush. However, I think we're in an era of wide, wide pendulum swings.
At 57, I'm barely old enough to remember "stumblebum Ford", and the peanut farmer for Georgia. Also really stretching things with attacks on Reagan, and then much of the same (but to a lesser degree) with Clinton. Most here remember bad taste attacks on Bush. Sure, there was some outrage from "the other side" but not nearly to the degree of today, where a "bad taste" protest ends in job loss and even criminal charges.
The difference between then and now, IMO, is Obama. When he got in, the pendulum swung WAY to the "never attack the president" side. Partially because of his race, partially because it was the dawn of the modern SJW, likely for other reasons I can't think of. The point is that we hit a time where the SJW "I can say whatever I want, but you can't because it's hate" mantra came into full swing. So certainly while what Griffin did is free speech, the outrage from regular America is really less aimed at attacks on Trump as it is on the past outrage and response to much less volatile attacks on Obama.
So less to do with attacks on the president, and more on the SJW mentality. IMO anyway.