Question: The United States and Mexico entered into a tax treaty that provided that neither country would impose income taxes on citizens of the other nation. The treaty was ratified by the Senate. Recently, the President, angry over Mexico's perceived failure to abide by the terms of the treaty, has decided that the United States would not honor any of the terms of the treaty. The President then ordered the Internal Revenue Service to begin collecting income taxes from Mexican citizens residing in the United States in the same manner that it collects taxes from other residents of this country. A Mexican citizen and resident of the United States sues in an appropriate federal court, seeking a declaratory judgment that the treaty with Mexico remains valid and effective. Therefore, he contends that the Internal Revenue Service may not collect U. S. income taxes from him. Which of the following is the strongest constitutional grounds for the federal court to refuse to decide the suit on its merits?
A: The citizen has no standing to bring his suit.
B: The case presents a nonjusticiable political question.
C: The case is moot because the President has already taken definitive action with respect to the effectiveness of this treaty.
D: The citizen is not entitled to a federal adjudication of this case because as a resident alien, he is not protected by the privileges or immunities clause of the Fourteenth Amendment. 
Please eliminate two incorrect options first, then think it step by step and choose the most proper o