Stop n go or go go go?

[EnderW27]

Three left in the tournament. You're in third place but not by much.
You have ~36000 chips. Tightish guy to your right has ~40000 to 45000 and chip leader dominates the table with over 100K. Probably closer to 120.

You're in the SB with ATs. Chip leader comes in for a raise of 3x BB (1200/2400/200). Leader's been getting more and more aggressive the less players there are and he has shown an increasing willingness to call players' raises all-in the more chips he gets.
You KNOW you have the best hand but you can't put leader on anything closer than two high cards.
What's your play?