Four key takeaways from the Supreme Court's travel ban ruling

It is obvious that the U.S. Supreme Court's decision to uphold President Donald Trump's "travel ban" divided the justices along the standard ideological lines. But there is a lot that is less than obvious in the multiple opinions, extending to some 92 pages.

Here are four points that have big implications for the future.

1) Korematsu vs. U.S., decided in 1944, upheld a presidential order calling for the forcible relocation of Japanese-Americans to concentration camps. The decision has never been overruled. In recent years, some people have insisted that it is still good law and that it might be used as a precedent to support presidential efforts to combat terrorism.

Speaking for the 5-4 majority, Chief Justice John Roberts repudiated Korematsu. He declared that the relocation order was "morally repugnant." He added that the case was "gravely wrong the day it was decided" and that it "has been overruled in the court of history."

True, Roberts was responding to the charge, made by Justice Sonia Sotomayor in dissent, that his opinion should be seen as this generation's Korematsu. But whether or not she's right, the court's repudiation of that ruling is major. It offers a clear warning to future presidents, and also to the current one.

2) Justice Anthony Kennedy, who provided the crucial vote, seemed agonized about the case. In a short concurring opinion, he emphasized that all officials, including the president, are bound by the Constitution — even if courts are reluctant to invalidate their actions.

Here are his words: "The oath that all officials take to adhere to the Constitution is not confined to those spheres in which the Judiciary can correct or even comment upon what those officials say or do." Seeming to speak directly to the White House, he added: "An anxious world must know that our Government remains committed always to the liberties the Constitution seeks to preserve and protect, so that freedom extends outward, and lasts."

These words are obviously heartfelt. But in the context of the travel ban in particular and contemporary concerns more broadly, they're pathetic.

Sure, the president is bound by the Constitution. But if the Supreme Court will decline to safeguard "the liberties the Constitution seeks to preserve and protect," an anxious world will not be comforted.

3) For many decades, the justices have struggled with the "rational basis" test, sometimes used to strike down acts of government as arbitrary. Kennedy has insisted that the test is really a ban on "animus" of the kind that can be found when the government discriminates against politically unpopular groups.

Roberts embraced Kennedy's thinking. He made it clear that if the president had been shown to have acted on the basis of animus, the travel ban would have to be struck down.

For that reason, he worked hard to explain why no animus had been shown and why a legitimate national security interest justified the ban on travel from seven countries, five of them predominantly Muslim. Whether or not his argument is convincing, Roberts left considerable room for future challenges whenever the government seems to act on the basis of hostility to politically unpopular groups.

4) Justice Stephen Breyer wrote a modest, careful opinion, joined by Justice Elena Kagan, that almost certainly would have commanded a majority if the Republican Senate hadn't blocked the nomination of Judge Merrick Garland (chosen by President Barack Obama in 2016 to fill the seat vacated by the death of Justice Antonin Scalia). In Breyer's view, the only question was whether Trump's travel ban proclamation was really an effort to protect national security or was significantly influenced by animus against Muslims.

Breyer pointed out that as it is written, the proclamation contains an elaborate system of waivers and exemptions, which allow case-by-case judgments about people who might qualify for visas. Breyer thought it essential to ask: Are exemptions and waivers being given to people who do not pose a national security threat?

As it happens, the number of waivers has been minuscule. Numerous applicants — people requiring medical treatment, academic visitors, students, family members, children — are not easily seen as national security threats. And yet they haven't been getting waivers.

In light of this, Breyer said that he would have sent the case back to allow the government an opportunity to explain itself, while leaving in place the lower courts' injunction against the ban.

Breyer's opinion doesn't have the passion or eloquence of Sotomayor's powerful dissent (joined by Justice Ruth Bader Ginsburg). But because of its quiet commitment to reason-giving and the rule of law, it has a claim to stand among the most distinguished dissenting opinions in the history of the Supreme Court.

It is important to acknowledge that Roberts' opinion is also careful and disciplined; he does not give a blank check to Trump or his successors. Nonetheless, American ideals have taken a beating. For the future, Breyer's opinion stands as a beacon of light.

Cass Sunstein is the editor of "Can It Happen Here? Authoritarianism in America" and a co-author of "Nudge: Improving Decisions About Health, Wealth, and Happiness."