COH, I'm sorry, but that's just silly. FBI background investigations are not oppo research. Background investigations aren't about looking for good stuff - it's about looking for red flags and problems. I've had an initial background investigation and periodic background investigations since 1985. I was asked a lot of tough questions over the years. Of course they ask questions about my personal life. That shouldn't be off limits for a person who's going for the highest possible security clearance (which I held and still hold). Sometimes I wonder how in the hell they found certain things which I considered a bit embarrassing.
Ultimately, I "passed" and retained my clearance every time. These things are supposed to be thorough looks, and I see absolutely nothing unusual in what we know about his. I also think the idea that the FBI is bringing politics into this to be ludicrous.
Incidentally, promising not to drink if confirmed is a large red flag.