Petraeus was a potential GOP nominee for 2012.
Obama’s team does great opposition research (using the FBI).
The Obama team plays chess well.
Obama named Petraeus to CIA because he was known as a man with integrity, and it kept him off the VP list for 2012. The real question will be, how long has the FBI known? Did they find out during his vetting, (they would have asked him) or did it subsequently come to their attention. And what foreign intelligence agencies knew? Iran, Pakistan, Muslim Brotherhood? That would be more disturbing.
The double standard is this: If Petraeus were a Democrat, this whole thing would blow over (no pun intended) and he’d be ready to run for office by the next election cycle (think Clinton, Barney Frank, Elliot Spitzer, etc). But as a Republican, he’s pretty much done, I would expect.
Petraeus was never going to be a GOP nominee for anything. His wife works in the Obama White House.