Your system engineer has started making negative commen during your weekly team meeting. He has had a heated argument with the marketing manager, and you have heard fro various team members that he has become difficult to work wit What is the best course of action for you to take?

A $0$

You should confront the system engineer openly a the next team meeting. Let him know that his behavior is unacceptable and that he will be replaced if there is not an immediate change.

You should schedule an individual meeting with the system engineer to determine whether he has issues with the project that need to be resolved. Get his perspective on how the project is progressing and how he feels about his role.

You should write a memo to the system engineer's functional manager and request a replacement as soon as possible.

The system engineer is critical to the project, so you should give him some slack and wait to see whether the behavior stops.