Last week, President Barack Obama gave his farewell address. Today is his last full day in office. Now is therefore an appropriate time to begin to assess his legacy, including his legacy for American constitutional law.

Any such early assessment must be provisional, at best. We do not yet have sufficient historical distance from Obama’s time in office to reach anything approaching definitive conclusions. Still, we can at least make a start.

Obama deserves credit for helping to push the struggle for same-sex marriage to a successful conclusion, for appointing some highly capable judges (despite flaws in their judicial philosophy), and for causing the Supreme Court to establish some valuable precedents protecting federalism, property rights, and religious freedom (albeit, often unintentionally). On the other hand, we may well have occasion to rue his overly expansive approach to executive power, particularly when it comes to initiating wars without congressional authorization.

I. The Loaded Gun Obama Will Leave Trump.

Perhaps the most important constitutional legacy of the Obama administration is one that does not get nearly as much attention as it deserves: by starting two wars without the constitutionally required congressional authorization, Obama established dangerous precedents that can be used by Donald Trump and other potentially unscrupulous successors. In the case of both the 2011 war against Libya and the still-ongoing war against ISIS, Obama relied on flimsy legal pretexts to to initiate wars.

To his credit, Obama has since admitted that the Libya intervention was his “worst mistake.” But he still refuses to recognize that it was unconstitutional, or that its dubious legal rationale had any connection to the sorry outcome.

In both the Libya and ISIS conflicts, the Obama administration stopped short of claiming, in the fashion of John Yoo, that the president has unlimited inherent power to start wars. But the rationales they relied on instead are not much better. In the Libya case, for example, the administration advanced the ridiculous theory that the Libya conflict was not a real war (or even a case of “armed hostilities” covered by the War Powers Act) because “U.S. operations [in Libya] do not involve sustained fighting or active exchanges of fire with hostile forces.” You don’t have to be a law professor like Obama to understand that launching numerous air strikes for the purpose of overthrowing a government qualifies as war, and certainly as “armed hostilities.” If it does not, all sorts of other large-scale military interventions can be justified on similar grounds. Similar problems arise from the administration’s attempts to stretch the 2001 and 2002 congressional authorizations for the use of military force to cover the conflict against ISIS. These too are holes that Donald Trump – or some other future president – could potentially drive a truck through.

Obama’s actions have, quite literally, left Trump a loaded gun he could potentially fire almost any time he wants to. Actually it’s an entire army of loaded guns, to say nothing of loaded missile launchers and aircraft carriers. Hopefully, Congress will reassert its constitutional authority over this important field. Principled lawmakers like Democrat Tim Kaine and Republican Rand Paul would like to do just that. But I am not as optimistic as I wish I could be that their counsel will be followed. Most members of Congress – and most of the general public – seem happy to continue ignoring this issue.

The constitutional requirement of congressional authorization is not just a legal technicality. It also helps protect us against initiating dubious conflicts at the behest of a single man, and increases the likelihood of success in those wars we do choose to fight.

President Obama would have done better to stick to the principle then-Senator Obama stated in 2007: “The President does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.” We may yet have occasion to lament his failure to live up to his own principles here.

Obama’s overextension of executive power to initiate war was the most dangerous example of numerous similar abuses in other areas, many of them chronicled in my George Mason University colleague David Bernstein’s book on the subject.

I don’t agree with all of the conservative criticisms of Obama’s executive actions. And some had precedents in similar abuses by previous presidents, including Republican ones. But the overall picture is still not a pretty one, and still creates dangerous precedents.

II. Victory in the Struggle for Same-Sex Marriage.

Obama’s term in office coincided with the dramatic final victory the struggle for marriage equality, which culminated in Obergefell v. Hodges, the Supreme Court’s2015 decision striking state down laws banning same-sex marriage. Obama’s role in this battle was somewhat equivocal, but nonetheless crucial.

For a long time, Obama led the fight for marriage equality from behind, to adapt a notorious phrase from the Libya conflict. He spent years pretending to be opposed to same-sex marriage even though he was actually in favor of it. But when he did finally reveal his true position in 2012, it helped coalesce public and elite opinion in favor of same-sex marriage, ultimately leading to the Supreme Court decision in its favor. Given the Supreme Court justices’ sensitivity to public opinion such a high-profile issue (which may have caused them to duck it when it first came to the court in 2013), it seems unlikely that the Court would have struck down all state laws banning same-sex marriage if the nation’s popular liberal Democratic president were still officially against it. Moreover, Obama appointed two of the five justices who voted with the majority in Obergefell.

While Obergefell was a close 5-4 decision, it has rapidly achieved widespread public acceptance, to the point where it barely registered as an issue in the bitter 2016 presidential campaign, and Donald Trump says that it is settled law that should not be overruled.

In my opinion, Obergefell was a correct decision, albeit poorly reasoned. Many will dispute one or another of those characterizations. Be that as it may, the ruling is likely to be a lasting part of Obama’s constitutional legacy. More generally, the Obama era may well be remembered as the time when gays and lesbians became fully equal citizens to a much greater extent than ever before. Obama deserves considerable credit for that, even if his performance was far from a profile in political courage.

III. Obama’s Impact on Supreme Court Doctrine.

The Obama administration’s policies led to some major Supreme Court decisions, many of which changed legal doctrine for the better. By far the most high-profile of these cases were a series of rulings involving challenges to the president’s signature legislative achievement, the Affordable Care Act. In NFIB v. Sebelius (2012), the Supreme Court upheld the ACA’s health insurance mandate by reinterpreting it as a “tax,” but also set important limits on Congressional power under the Commerce Clause and Necessary and Proper Clause. On the latter issue, the Court provided the most through analysis of the meaning of “proper” (and the way it limits federal power) that it had ever issued in 200 years of case law. NFIB also partially struck down the ACA’s Medicaid expansion, thereby providing the first Supreme Court ruling limiting Congress’ spending power, in over 75 years. This unexpected ruling – joined by two of the Court’s liberal justices, including Obama appointee Elena Kagan – was an important part of of a more general revival of constitutional federalism in the Roberts Court.

The long-term impact of NFIB is still unclear. But I tentatively predict that these limits on federal power will ultimately prove more significant than Chief Justice John Roberts’ awkward attempt to reframe the mandate as a tax. Liberals -including President Obama himself – decried the pro-federalism elements of the decision at the time. But they may have reason to take a different view of constitutional federalism under Trump.

In 2015, the Supreme Court, ruled in the administration’s favor in King v. Burwell, thereby saving Obamacare subsidies for people purchasing health insurance on federal exchanges established in the many states that refused to set up state exchanges. The case was a major victory for the administration. But the Court also reaffirmed the principle that courts should not defer to executive agencies’ interpretations of law on major questions, instead making their own decisions on such issues. That could help curb executive power in the future.

In Burwell v. Hobby Lobby Stores, yet another ACA case, the administration suffered a notable defeat when the Court ruled that commercial firms can assert rights to religious free exercise under the Religious Freedom Restoration Act. Although the case was not directly focused on constitutional issues, its reasoning offers important protection to people using the corporate form more generally, including with respect to their ability to assert constitutional rights.

While I disagreed with many of the Obama administration’s positions in the various Obamacare cases, I also recognize that most of them were at least plausibly defensible. Even when the administration lost on key issues in these decisions, it was usually on a close vote split along ideological lines.

The same can’t be said for many of the arguments the administration advanced in numerous property rights cases, which were so extreme that they resulted in a series of lopsided 9-0 and 8-1 defeats in the Supreme Court. The most recent was Horne v. Department of Agriculture II, the famous raisin takings case. These decisions led to a notable strengthening of judicial protection for constitutional property rights under the Takings Clause – the very opposite of the result the administration probably hoped to achieve.

There is a similar story to be told about Hosanna-Tabor v. EEOC, an important religious freedom case in which the Obama administration also adopted an extreme position that led to a unanimous ruling protecting the right of religious institutions to choose ministers free of restriction by antidiscrimination law. Here too, the administration ended up helping its adversaries.

In sum, advocates of constitutional federalism, property rights, and religious liberty have reason to be grateful for the Obama administration’s efforts in these fields. They would have been hard-pressed to gain so much ground otherwise. But President Obama himself probably doesn’t want the credit.

IV. Obama’s Judicial Appointments.

As with any president, Barack Obama’s judicial appointments are likely to be among his most lasting legacies. President Obama appointed two Supreme Court justices – Elena Kagan and Sonia Sotomayor – and hundreds of lower court judges. Many of these judges will continue to serve for decades after President Obama leaves office. For that reason, their full impact is difficult to predict at this point. So far, Obama’s judicial appointees are notable for their impressive professional skills, their racial and ethnic diversity, and their near-uniform adherence to liberal orthodoxy on most major constitutional issues. That uniformity has moved many lower federal courts significantly to the left of where they were when Obama took office.

Few can doubt the value of having judges with solid professional skills, and there is also some value to having judges from a wider range of racial and ethnic backgrounds. Whether we should approve of the Obama appointees’ judicial philosophy is a question that splits commentators along predictable ideological lines.

What is true of the Obama judges generally is also true of his two Supreme Court appointees, justices Kagan and Sotomayor. Both have impressive professional skills, and both are predictable liberal votes on most major issues.
I myself take a more favorable view of Kagan (whose nomination I supported) than Sotomayor (whom I testified against, because of her record on property rights issues). So far, both have performed on the Court more or less as I would have expected: voting similarly on most issues, but with Kagan showing greater open-mindedness and less tendency to dismiss opposing views in ideologically charged cases.

On one additional point both Kagan and Sotomayor deserve praise: neither has turned out to be a mere rubber-stamp for the president who appointed her. Both have voted against the Obama administration on some important cases, including several of the property rights and religious liberties cases described above. The two justices deserve credit for their independence, and the president himself deserves some credit for appointing people with that sort of integrity.

But the jury is still out on both of these justices. Kagan and Sotomayor may be on the Supreme Court for many years to come, and their most important decisions might well lie ahead of them.

I end this essay where I began: It is still too early to make any definitive judgment on Obama’s constitutional legacy. Years from now, it might look very different than today. If Donald Trump turns out to be as bad as I and many others fear, Obama’s legacy might come out looking good simply by virtue of the inevitable comparison with his successor. If, by contrast, Trump is perceived as a success, Obama’s reputation might suffer accordingly. And if Trump or another successor misuses the dangerously broadened executive powers Obama leaves behind, Obama will deserve a share of the blame.

For now, all we can say for sure is that Obama’s presidency is likely to have a lasting impact on American constitutionalism. It is not yet clear whether its bad effects are likely to outweigh the good. We should hope for the best. But, as Obama himself put it, “[h]ope is not blind optimism. It’s not ignoring the enormity of the task ahead or the roadblocks that stand in our path.”

This piece was originally published at The Volokh Conspiracy at the Washington Post website.