Rosenstein, AKA Mr. Peepers according to Trump, simply took out an insurance policy for his government pension by blowing all that smoke up Trump's considerable ass.
Maybe McCabe and Rosenstein were friends, maybe not. But the lesson of Trump's pettiness toward McCabe was certainly not lost on Rosenstein.
I'd say wait for Rosenstein's book but we already have enough books accurately describing Trump as the fucking idiot and sociopath he daily demonstrates that he is.