How bad can be that move? I would normally rarely 3bet with AJo in that situation but I wanted to experiment with ranges. AJo is definetely borderline but against a fairly LAGgro villain (36/18 over 55 hands, rather passive postflop, has been active for the last couple of hands) should be +ev.
Exactly villain dependent. So in this situation get it in. And look at his stack size, his raise to 400 is much less scary than if he made the same raise with a 2K stack. Here it's looking like he's planning to raise-fold vs some / raising "because he can afford to".