Hawaii and several other states and groups challenged the Proclamation and two predecessor executive orders also issued by Trump on statutory and constitutional grounds.

Citing a variety of statements by Trump and administration officials, they argued that the proclamation and its predecessor orders were motivated by anti-Muslim animus.

[1] A U.S. district court issued a preliminary injunction preventing the ban from coming into effect, finding that plaintiffs were likely to succeed in their argument that the proclamation violated the Establishment Clause of the First Amendment to the United States Constitution and exceeded the president's powers under the Immigration and Nationality Act (INA).

The decision, written by Chief Justice John Roberts, applied rational basis review and emphasized deference to the executive branch.

In addressing the travel ban, the Court also repudiated the infamous decision Korematsu v. United States, 323 U.S. 214 (1944), which had justified the president's powers to establish internment camps for Japanese Americans during World War II.

The forcible relocation of U.S. citizens to concentration camps, solely and explicitly on the basis of race, is objectively unlawful and outside the scope of Presidential authority.

[3] As part of his immigration policy, United States President Donald Trump had sought to limit foreigners from certain countries from traveling into the U.S. On January 27, 2017, he signed Executive Order 13769 (EO 13769), which banned entry to citizens of Iran, Iraq, Libya, Somalia, Sudan, Syria, and Yemen for 90 days regardless of their visa status, and suspended the United States Refugee Admissions Program (USRAP) for 120 days.

Watson wrote: "When considered alongside the constitutional injuries and harms discussed above, and the questionable evidence supporting the Government's national security motivations, the balance of equities and public interests justify granting the Plaintiffs.

Equally flawed is the notion that the Executive Order cannot be found to have targeted Islam because it applies to all individuals in the six referenced countries.

[13]: 31 In drawing its conclusion, the Court quoted the Ninth Circuit appeal ruling on the original Executive Order (13769): "It is well established that evidence of purpose beyond the face of the challenged law may be considered in evaluating Establishment and Equal Protection Clause claims", and quoted previous rulings that "Official action that targets religious conduct for distinctive treatment cannot be shielded by mere compliance with the requirement of facial neutrality" (Church of the Lukumi Babalu Aye v. City of Hialeah); "a facially neutral statute violated the Establishment Clause in light of legislative history demonstrating an intent to apply regulations only to minority religions" (Larson v. Valente); and that "circumstantial evidence of intent, including the historical background of the decision and statements by decisionmakers, may be considered in evaluating whether a governmental action was motivated by a discriminatory purpose" (Village of Arlington Heights v. Metropolitan Housing).

[13]: 32  The Court also took into account numerous statements by the president and his team, before and after election, that directly said that he sought a legal means to achieve a total ban on Muslims entering the U.S.,[13]: 33–37  and a "dearth" of substantive evidence in support of the stated security benefits.

Judge Kozinski of the Ninth Circuit Court of Appeals filed a late dissent on March 17, 2017, to the Ninth Circuit's opinion in Washington v. Trump, arguing against the State of Washington's Establishment Clause claims on grounds that Trump's words during the campaign were political speech protected by the First Amendment.

[23][24] Acting Solicitor General of the United States Jeffrey Wall and Hawaii's attorney, Neal Katyal, appeared before Circuit Judges Ronald M. Gould, Michael Daly Hawkins, and Richard Paez for an hour of oral argument in Seattle's William Kenzo Nakamura United States Courthouse.

But the court also found that Watson should have avoided the constitutional question and should not have enjoined the purely internal government vetting review.

[28] On June 19, Watson complied with the Ninth Circuit's decision and revised the injunction such that it would exempt "internal review procedures that do not burden individuals outside of the executive branch of the federal government".

[31] On June 29, Trump sent out a diplomatic cable to embassies and consulates seeking to define what qualifies as a "bona fide relationship", excluding connections with refugee resettlement agencies, and clarifying that step-siblings and half-siblings are close family while grandparents and nephews are not.

[34] On July 19, the Supreme Court left Watson's order on family definitions in place but stayed while on appeal the part of his injunction on refugee resettlement agencies.

The decision lifted the injunction against the travel ban's enforcement and remanded the case to lower courts for review of other arguments the plaintiffs raised.

[53] Plaintiffs argued that it did, due to the president's statements about Islam, which may have put in doubt that the federal objective did not specifically target a religion.

If religion is targeted intentionally, then strict scrutiny review applies, which requires the government to show that the act was necessary to meet a compelling governmental interest.

The court held that the travel ban did not violate the Free Exercise Clause because his statements could be reasonably understood to be justified independent of unconstitutional grounds.

[50] Part of the majority's decision referenced Korematsu v. United States, 323 U.S. 214 (1944), which upheld the constitutionality of President Franklin D. Roosevelt's Executive Order forcing Japanese-American citizens into concentration camps during World War II.

If this Court must decide the question without this further litigation, I would, on balance, find the evidence of antireligious bias...a sufficient reason to set the Proclamation aside.

[60]Sotomayor took issue with a perceived double standard by the Court given the decision in Masterpiece Cakeshop v. Colorado Civil Rights Commission, 585 U.S. 617 (2018), which found that government officials had treated a defendant's freedom of religious exercise with hostility, demanding the case be reheard on a more neutral basis.

[61] Sotomayor also saw parallels between this case and Korematsu, acknowledging that decision's legacy and the cautions that the dissenters from it had made about the threat to the Constitution as a result.

"[1] After the decision, various protests were held around the country, including one in front of the Supreme Court building in Washington, D.C.,[62] and others in New York City, Seattle,[62] Portland,[63] and Atlanta.