This is a great leadership question. The answer? Put the Soldier in charge. Make him responsible for the solution. One of two things could happen:
- They might actually do a good job, solving the problem and delivering a sound solution. In this scenario, everyone wins. Now you just need to have discussion with the Soldier about how his constant complaining is bad for morale, creates friction, and will no longer be tolerated. If he has suggestions that contribute to the unit in a meaningful way, listen to them. If he has nothing positive to contribute towards solving the issue then he needs to remain silent.
- Otherwise, he will screw up the task or execute it in a substandard manner. In this case, you will want to conduct a professional after action review. Suggest that he should offer solutions before offering complaints in the future. He should also understand that being responsible means being held accountable. Being a critic is always easy. Perhaps he should begin to contribute rather than criticize. If you can deliver this message in a positive professional manner you will probably hit a nerve. Because he complained in the past, was placed in charge, and did not do well he lost credibility. Therefore, he will need to find a way to reestablish himself. You can use this to your advantage and motivate him to become a productive team member.
Remember: When in charge, take charge. When not in charge let those in charge be in charge!