Whether the beneficiaries could invoke the Due Process Clause to challenge Florida's jurisdiction over the absent Delaware trustee.
Holding
Yes. Because Florida law treated the trustee as an indispensable party to an action affecting the trust's validity, parties affected by the judgment had a direct and substantial personal interest in whether Florida acquired jurisdiction over the trustee.
Reasoning
Ordinarily, a litigant may not assert a third party's constitutional rights. But Florida's own law required the presence of a trustee before a court could adjudicate a controversy concerning the validity of a trust. If the trustee was beyond the court's jurisdiction, the Florida court lacked authority to proceed at all, including against parties who were otherwise properly before it. That gave the beneficiaries a sufficient personal stake to raise the jurisdictional defect.