I think Obama is completely sincere in at least considering making this offer (and as I understand it, he did not ask her to be, just if she would be at all interested in the job). Clinton may not have extensive diplomatic credentials personally, but she is well-known throughout the world, and has remarkable star power - not as great as Obama’s own, but pretty darned good. Her husband is enormously popular around the world, and I assume that would start her off with quite a bit of good will on the not unreasonable basis that she would hold views not entirely dissimilar to those of her husband.
But mostly, I think Obama is quite consciously imitating the man he considers to have been his role model, Lincoln. Hence his consideration of Hillary, and his meeting today with John McCain. Look, in his quiet, diplomatic way, Obama is the most dominant man I’ve ever seen, if only because he listens to everything everyone says courteously, and then goes away to make up his mind. That’s an enormously effective technique, and it really prevents people from playing politics, because it’s so hard to get a read on him. You can’t tell what sways him if he doesn’t ever seem to be swayed.
So I’m really not worried about the Clintons, although I used to be. Obama’s not going to be fashed by little stuff, or at least his history shows that he’s very tolerant of people’s foibles as long as they do a good job for him. So if Bill wants to spout off and it doesn’t do Obama or the country any actual harm, Obama will deal with it. If Hillary starts making her own policy (which I strongly doubt she would do; she’s far too well-disciplined to do that), she’ll probably be reprimanded quietly. Once. That would be my guess, anyway. They both want what’s best for the country, and there’s not a huge policy difference between them anyway, so I don’t see its happening as very likely.
I like Richardson myself, but I can see the advantages to having Hillary, and I certainly can see the advantages to asking Hillary. It’s a signal of strength, not of weakness. But then, for all the country’s in a really bad way right now, Obama is in about as good shape politically as it’s possible for a president to be at this stage in the game, according to the polls, so he’s got a lot of strength. He might as well use it; it’s not like it will hang around forever if he stashes it under the mattress.