Assigned to a project with tight schedule and costs, the project manager finds there are insufficient resources. What should the project manager do?

The project manager's primary responsibility is to achieve project objectives. When facing insufficient resources, the most proactive and effective first step is to identify the specific resource requirements and formally communicate these needs to relevant stakeholders. This allows stakeholders to understand the impact and potentially provide the necessary resources or adjust expectations. Updating the risk register is a reactive step that doesn't address the immediate problem of resource shortage. Creating a WBS and reducing project management activities are not appropriate responses; the WBS is a planning tool, and reducing project management activities would likely increase project risk. Formalizing a scope change request might be a later option if resources cannot be obtained, but the initial action should be to attempt to secure the required resources.