Yes, there is not a guarantee, but the goal of these consensus mechanisms is to make the cost of attack greater than the reward. In order for a successful atta

Yes, there is not a guarantee, but the goal of these consensus mechanisms is to make the cost of attack greater than the reward. In order for a successful attack, I believe you'd need to control a very large portion of all available REP. If your attack is successful, the value of your REP would likely go down (as the market is no longer trusted) so there's likely no economic incentive to do such an attack.