Mightn't

It mightn't have been my youngest brother's fault, but it wasn't mine either.

Her driver was new to the country; he mightn't be prepared for the leaping of the yellow water down dry arroyos, swift as the pouncings of a cat, or the snake-like slidings of tons of loosened rock and clay from the steep potreros […]

“But, mightn’t there have been something unusual about the Stimatis contract itself?” [Perry Mason cross-examining Roger Correll.]

"But at night she would still think the same thing: mightn't it be that he wouldn't come to see her anymore?"