I'm no fan of Trump, I detest the man - president or not.
But I don't think he was dog whistling, or at least he is dumb enough not to realize the significance of the comment. He could easily have been trying in his subtle and nuanced way to insult the Dems.
I could be wrong, but I think Trump just doesn't care, he says whatever comes into his head and due to his background and personalty sometimes this means he is misogynistic or racist or homophobic etc. I recon he's not spending all his time in private preoccupied with ensuring white privilege. I think he makes of the hip decisions if he thinks it will make him popular with whatever crowd he is talking to at the time.
Due to his obvious lack of empathy, intelligence, sophistication in the way he thinks and talks it wouldn't have even crossed his mind that the comment was bad in another way other than the way it was intended to be bad.
If he did make the comment intentionally because of its undertones, then he's not the ignorant clumsy person I thought he was, he's more of a calculated intelligent nasty dangerous person.