is it legal to drive with a BAC under the legal limit?

The hamsters arte your OP. But assuming the question was in the title, the answer is yes, that’s what “legal limit” means.

That’s a tricky question. You’d have to go state by state to see the specifics of the laws but consider that some states make it illegal do drive while impaired no matter what your BAC is. Just because you haven’t broken one specific law doesn’t mean that everything you do is legal.

Padeye nailed it for Minnesota. Minnesota is one of the few States, ie. less than 5, which still have the .10 impaired limit. However, as Padeye so wisely advises, you can still be convicted for careless driving with a BAC under .10. Some insurance companies equate a careless driving conviction with a DWI/OWI because DWI/OWI first timers with a low test score (.10-.12) frequently plea bargain to a careless driving conviction. Minnesota considers you in control of the vehicle and subject to a DWI charge even when you are sitting in it, parked in your home driveway, with the vehicle’s key in your pocket. I read a case our Court of Appeals decided which upheld the DWI conviction of a man that partied at a rock concert, crawled into his pickup at a parking ramp to sleep it off, and was convicted of DWI since he was sleeping in the truck with the key on his person. That said, we CAN drive our scenic highways etc. with an open can of non-alcohic beer in the drivers hand. Ain’t law grand?