If π (Tennessee) sues ∆ (Idaho) and ∆ impleads T (Idaho), what is the reason for jurisdiction under supplemental rules?

The correct answer is centered around the concept of supplemental jurisdiction, which allows a federal court to hear additional claims that are related to the original complaint. In this scenario, the plaintiff (π) from Tennessee has sued a defendant (∆) from Idaho, and the defendant has brought in a third party (T) from Idaho through the process of impleader.

The key reason for asserting supplemental jurisdiction in this case is that the claims against the third-party defendant (T) arise from the same transaction or occurrence as the original action. This connection is essential; supplemental jurisdiction is typically granted when the additional claims are closely related to the claims already before the court, which promotes efficiency and judicial economy by resolving all related disputes in one proceeding.

In this context, a claim that arises from the same transaction or occurrence means that it involves the same facts or events that led to the initial lawsuit, providing a basis for the federal court to assert jurisdiction over the additional parties involved. This rationale is pivotal in ensuring that the court can comprehensively address the issues at hand without requiring separate lawsuits in potentially different jurisdictions.

The other options do not apply in this specific scenario. For example, the existence of a federal question relates to subjects that fall under federal law, which is