As difficult as this situation is that is, I believe that the greater concern is not the competition or the economic environment. Rather, it is the enemy within. I am not referring to any kind of industrial sabotage or cyber-spying because the enemy that concerns me is usually wears the same company ID. And therein lies the problem...they are hiding in plain view.
I am referring to the person who sees themselves as a leader...without portfolio. They want to make decisions, not follow them. They view those in leadership roles as being out of touch or incompetent. Accordingly they have a personal agenda that dictates their behaviour. Left unchecked there are no limits to the damage that they can cause because it is not simply a matter of their response but also the influence that they may hold over others. In these cases it is true that one bad apple can spoil the whole basket.
There are several reasons that someone may take on this 'anti-leader' persona. Some people feel as though they have been passed over for promotion and look to use their current position and influence in a subversive manner to cause the leader to fail. In this way, the individual hopes for an opportunity to replace the leader and thereby assume their 'rightful' position.Sometimes the person genuinely wants to support the leader and feels that taking a different strategy is actually helpful. In principle they disagree with the leaders approach but they do not dislike the person and therefore they view their actions to be supportive and not subversive. The end game is not personal recognition; it is to prevent failure. And in some instances the individual actually takes on the role of enemy. For any number of reasons this person wants to cause as much damage as possible before being found out and dismissed.
If any of these situations exist in your organization, you must address it aggressively and proactively. The impact of this subversive type of behaviour is seldom limited to that which is obvious. If the individual is otherwise liked and respected, it is probable that the consequences of their behaviour will have roots in several areas. You must identify the extent of the impact to ensure that no residual damage remains.
As part of the remedial action - which has probably resulted in a termination - the leader should perform an unbiased appraisal of the environment that fostered this act of betrayal. That is not to suggest that someone had just cause to be subversive. But clearly something prompted this most vile kind of insubordination. It is not enough to rid the organization of these actions. It is equally important to ensure that any aspect of the company's policies, procedures or environment that may have contributed to these actions are fully addressed and amended. If that means a corporate 'mia culpa' so be it. This is not the time to take pride in having solved an issue. The enemy within is seldom a fluke and will return if the proper remedial action is not properly implemented.
An engaged leader will spot the problem early enough to mitigate damage. An aloof manager will have a difficult time even acknowledging that a problem exists. Which best defines your style?