Final answer:
The Supreme Court disagreed with the federal government's argument that the DACA program is illegal.
Step-by-step explanation:
The sentence from the section "Second Ruling Against Trump In A Month" that best explains the rationale of the Supreme Court's DACA decision is: The justices disagreed with the federal government's argument that the DACA program is illegal.
This sentence indicates that the Supreme Court disagreed with the federal government's opinion that the DACA program is illegal. This disagreement suggests that the Court found legal grounds for supporting the DACA program and its protections for undocumented immigrants brought to the US as children.
The Court's decision to disagree with the federal government's argument demonstrates the court's role in interpreting and applying the law, and shows that the court believed the DACA program was legal based on their interpretation of existing laws.