If not: in general, in the US, it's perfectly legal for a company to just arbitrarily decide they need to fire N people, and arbitrarily choose a particular person to fire meet that "quota". This is true regardless of how many layers of managers are involved, or what bullshit PIP hoops are jumped through.

There would only be a legal issue if the worker was subject to a bona-fife employment contract (quite rare) or if they were discriminated against on the basis of a legally protected characteristic. Just being the least senior member of a team is not legally protected.