Charles M. Blow: We can’t afford not to prosecute Trump

We all learn from failure. Our mistakes become the bridge to our successes, teaching us what works and what doesn’t, so that the next time we muster the will to try, we’ll succeed. But nefarious actors can also learn from failure. And that, unfortunately, is where we find ourselves with Donald Trump. His entire foray into politics has been one of testing the fences for weaknesses. Every time a fence has failed, he has been encouraged. He has become a better political predator.