The political and spiritual forces upon Comey were incredibly powerful.
It was probably best that he stumbled in this fashion if he had to stumble. At least it is what some of the older humanists would have called “a cry for help.” One doesn’t just act like that unless one is being leaned upon a la the old USSR.
That would mean that if DJT actually suggested that Comey "let it go," he would have been trying to protect Comey from himself.