This is an awkward time to be finishing a book about war powers. As I complete it in late 2025, less than a year into Donald Trump’s second presidential term, the President is wielding military instruments in dramatic ways that test both the Constitution’s legal bounds and the nation’s political ones. He has ousted senior military officers, ordered heavy airstrikes on Iranian nuclear sites, and invoked an eighteenth-century wartime statute to detain and remove suspected “enemy” members of a foreign drug cartel. He has pushed past the limits of international law and the post-9/11 framework by authorizing lethal strikes on suspected drug vessels in the Caribbean and eastern Pacific, and he has threatened to carry such operations onto foreign soil – still without congressional approval. At home, he has federalized and deployed National Guard units to major cities over the objections of state governments. Indeed, it is hard to recall another moment, outside a major war, when a president wielded so many war powers for so many purposes at once. These moves have occurred alongside broader efforts to consolidate power in the Oval Office, including expanded use of emergency authorities, departures from long-standing norms of prosecutorial independence, and tighter White House control over regulatory agencies.

This book began by explaining that the Framers were at least as worried about the dangers that war powers posed to democratic self-governance as they were about the foreign policy risks. Many Americans feel the same today. In that sense, war powers have come back home – geographically, temporally, and civically.

It is too early to know whether this moment of strain marks an enduring shift in constitutional balance, a temporary detour, or a breaking point. By the time this book appears next year, the landscape will have shifted again – factually and legally. Years from now, perhaps these final pages will read less like an epilogue than an epitaph for the constitutional governance of war.

That uncertainty is not a deflection; it is the point of this book. The historical survey developed across these chapters shows that the war-powers system has not evolved linearly or predictably. Instead, it has been shaped and reshaped through repeated adaptation to changing security environments, as Congress, the President, the courts, and the states respond to one another’s moves. Two-and-a-half centuries of practice cannot predict what the war-powers system will look like when Trump leaves office, but they do offer perspective for judging this moment.

Some of Trump’s war-powers steps have clear precedents; all have precursors. In the republic’s first century alone, Washington’s militia call-ups, Monroe’s threats and cross-border raids, Jackson’s punitive expeditions, Polk’s politicized handling of his generals, Lincoln’s wartime detentions, and Andrew Johnson’s resistance to military Reconstruction each tested constitutional limits in their time. In the past century, so did Roosevelt’s internments, Truman’s Korean intervention and European deployments, Nixon’s secret bombings, and Bush’s terrorist detentions.

This comparison is not meant to equate or justify Trump’s actions. It is meant to show that his most controversial uses of military power often differ more in motive and magnitude than in kind.

That history also records precursors that never solidified into lasting practice. All presidents since Truman have used limited military force without congressional authorization, but no president has launched a major ground war without it or in defiance of a clear statutory prohibition. Presidents have been authorized by statute since the early republic to deploy militias (today’s National Guard) inside the United States, yet none has converted that power into a sustained and systematic means of federal control over the states. Nor, outside Reconstruction, have presidents employed the regular Army for that purpose or imposed martial law as a peacetime governing tool. Since the Civil War, no president has openly defied a court order on the claim that the Commander in Chief stands beyond judicial reach. Those are lines that Trump has not yet crossed. To do so would not merely test constitutional limits; it would rupture two centuries of practice and force a reckoning over whether law still meaningfully bounds the presidency.

Precedents and settled limits exist because competing institutional actors have established them through repeated interaction over time. At the present moment, the presidency looks imperial. Institutional checks look weak.

But past experience counsels patience as well as alarm about presidential powers; today’s snapshot may reveal little about tomorrow’s balance. The Framers’ experiment in war powers has, for much of American history, proven remarkably resilient. It often takes time, however, for other institutions to reassert themselves, as they did only after Union victories in the Civil War, deep into the Vietnam conflict, and gradually after 9/11. Checks that seem absent early in a conflict can reemerge later, taking many forms: legislation and judicial orders; major systemic resets, as after World War I and Vietnam; and subtler pressures, including resolutions, litigation threats, state-level resistance, and constitutional argument in the political sphere. Of course, greater interbranch involvement does not always restrain. It can reinforce, prolong, and intensify executive action, as it did during Lincoln’s wartime presidency, when U.S. nuclear strategy was taking shape, and for some aspects of the Global War on Terror.

Even as I write this, various institutional actors are responding to Trump’s exercises of war powers. Lawmakers have passed or proposed measures to slow or restrict certain military actions without Congress’s approval. They are also demanding briefings, legal justifications, or hearings to build political pressure or at least claim a seat at the policy table. Congressional scrutiny recently intensified amid allegations that a U.S. strike on an alleged drug vessel in the Caribbean may have been a war crime. Several states have successfully sued to block the President’s National Guard deployments, and civil-liberties groups have challenged his use of wartime removal authorities; those cases are now winding through the courts. These are early signs of checks, and just as Trump’s military moves will likely look different by the time this book appears, so will the legal landscape in which he operates – especially if control of Congress changes hands in the 2026 midterm elections. History teaches that whether Trump’s broadest assertions of war power endure will depend in part on whether they come to rest on a security and legal rationale that Congress and the public accept and courts decline to disturb.

Beyond those institutional dynamics, Trump’s actions underline that the most visible exercises of war powers – sending forces into battle or deploying them at home – often obscure the less visible ones: signals, threats, and assurances. He has openly threatened force in the Western Hemisphere, questioned or conditioned alliance guarantees, floated troop withdrawals from allied soil, and offered informal security promises to other partners. Presidents have long held vast power to wield such tools; unsurprisingly, Trump’s personal and transactional diplomacy has leaned heavily on them. But this book has also shown that Congress has its own ways – funding, oversight, policy declarations, and more – to influence how those tools are wielded. For example, Congress recently enacted measures to restrain the President’s proposed troop withdrawals from some allied territories. A clash over that move would invert many Framers’ original worries about executive adventurism and could raise unsettled war-powers questions about the powers to bring forces home. Strategic flux often begets constitutional flux.

During the nation’s first major foreign-policy predicament, the 1793 Neutrality Crisis, Hamilton observed that presidents shape the “antecedent state of things” – the security and diplomatic conditions that can seed or avert future conflicts and narrow Congress’s range of options. If the past is any guide, the most consequential effects of presidential power will not lie in Trump’s individual actions, but in the strategic settings they collectively establish – and in the patterns of response they elicit from Congress and the courts. Choices about international alignment, preparedness for particular contingencies, and the signaling of American commitments will shape which conflicts the United States confronts and which it avoids. Over time, these broad strategic choices will matter more than headline-grabbing interventions at home or abroad, both for the nation’s long-term security and for the durability of constitutional practices through which that security is pursued.