I disagree. It was a low-risk political move.
Bill wants Hillary to be President. The easiest/least risky path to that is going to be in a cycle where the incumbent President isn’t running. There’s no way of knowing whether a President Romney would gave had a successful first term, and Hillarys aging. The calculus was between running for sure in 2016, or risking a successful Romney first term and not having another real shot until 2020. With a reelection in 2024 and a Presidency ending in 2029, nearly 40 years after Bill became President.
No, the best shot for her was, and still is, a 2016 run to replace Obama.
That makes perfect sense, and is probably the case. If he hated Obama as much as they say now, would he have attached his stamp of approval and tied together his legacy with the Obama collapse? Would a disastrous second term of Obama do much to help Hillary when they ran in 2016?
Since they share 85% of Obama’s views, they probably didn’t think the later would happen, though. As a political whore, I am sure he had no concern about his mega-endorsement in 2012.