Craig Mokhiber, having resigned from his U.N. position and being a human rights lawyer, could indeed act as a lawyer in a case challenging the Biden administration's actions under Section 620I of the Foreign Assistance Act, provided:

1. Licensure: Mokhiber would need to be licensed to practice law in the jurisdiction where the case would be filed, typically in a U.S. federal court. If he is not currently licensed in the relevant jurisdiction, he would need to either:

   • Obtain a license through admission to the bar of that jurisdiction or,
   • Gain admission pro hac vice (for this specific case), which allows attorneys from other jurisdictions to practice in a specific case with local counsel.

2. Expertise: His background in international human rights law could be very relevant, especially if the case involves interpreting Section 620I in light of international law principles, humanitarian aid, and the legal implications of U.S. foreign assistance policies.

3. Ethical Considerations:

   • Conflict of Interest: If Mokhiber has any previous or ongoing relationships with parties involved that might create a conflict of interest, he would need to address this, possibly by withdrawing from any conflicting roles or obtaining waivers from affected parties.
   • Public Statements: His public statements, especially his resignation letter criticizing U.N. and international policy, might be scrutinized for bias, though in this context, they could also be seen as evidence of his commitment to the issues at hand.

4. Role in Litigation:

   • Representation: He could represent the plaintiffs directly or be part of a legal team.
   • Expert Witness: Alternatively, given his extensive experience and previous role at the U.N., he could serve as an expert witness providing testimony on human rights, international law, or the interpretation of Section 620I.

5. Resources: Litigation of this nature often requires significant resources, including time, legal research, and possibly funding for expert witnesses or travel for discovery. Mokhiber would need to ensure he has the support necessary to handle such a case.

6. Strategic Considerations:

   • Legal Strategy: He would need to strategize around overcoming potential barriers like the political question doctrine, establishing standing, and navigating the complexities of international law intersecting with U.S. domestic law.
   • Publicity and Advocacy: His involvement could also bring public attention to the issue, potentially aiding in advocacy efforts outside of the courtroom.

Mokhiber's profile as an experienced human rights lawyer with a focus on international issues makes him potentially well-suited for such a role, but the specifics of his participation would depend on his current legal status, ethical considerations, and the strategic needs of the case.