“It is the policy of the United States to not use nuclear weapons first.” This is the elegantly simple declamation of a bill, introduced on Wednesday by Representative Adam Smith, Democrat of Washington, the new chairman of the House Armed Services Committee, and Senator Elizabeth Warren, Democrat of Massachusetts, a member of the Senate Armed Services Committee. The proposed legislation would reverse the longstanding American policy of being theoretically prepared to initiate a nuclear conflict without first being subject to a nuclear attack.

Deterrence theory, which was adopted during the height of the Cold War, seemed to require that a country threaten its readiness to launch a preëmptive nuclear onslaught even before an enemy got to zero with its own countdown. Over the years, though, daylight fell between deterrence theory and strategic conduct. “No first use” became taken for granted as a matter of practice: the United States was not going to start a nuclear war. Barack Obama came close to turning that stance into policy late in his Presidency. Warned off by the national-security élite, including his own Secretaries of Defense, Energy, and State, who did not want to send softening signals to Russia and China, he declined to do so.

But the Trump Administration’s Nuclear Posture Review, issued a year ago this month, went fully the other way, openly declaring that the United States would launch nuclear strikes in response to “non-nuclear strategic attacks,” a vaguely characterized category that could be interpreted to include, say, cyber assaults on the American information infrastructure. Now, a readiness to use a nuclear weapon for the first time since the attack on Nagasaki is a central part of national-security doctrine, a perfect match to the Administration’s across-the-board bluster. First use is a readymade organizing principle for Donald Trump.

Smith and Warren are now openly defying that Trump doctrine. “No first use” can be understood as a kind of mantra, a symbol of a larger purpose—to move away from the decades-old paralysis of nuclear mania. That it could inhibit even a nuclear abolitionist such as Obama shows how multifaceted the problem remains.

Smith has introduced such a bill previously, but now he is joined by a colleague who stands at the pinnacle of the nation’s interest. Warren, who has all but announced a 2020 Presidential bid, embraced “no first use” in a major foreign-policy address at American University, in November, as one of what she called “three core nuclear-security principles.” The other two were “no new nuclear weapons” and “more international arms control, not less” —both of which point away from the road that the Trump Administration has taken. In renouncing the first-use doctrine, Warren joined an eminently practical concern—“To reduce the chances of a miscalculation or an accident”—to an ethical one. “To maintain our moral and diplomatic leadership in the world, we must be clear that deterrence is the sole purpose of our arsenal,” she said.

Introducing the No First Use Act marks a major move, for Warren, from the realm of rhetoric to actual lawmaking designed, at the very least, to prompt congressional consideration of a crucial national-security question. The Republican pushback came quickly. Senator Deb Fischer, of Nebraska, who chairs the Senate Armed Services Committee’s subcommittee on strategic forces, said that the proposal “betrays a naïve and disturbed world view.” Such dismissal will no doubt come from many quarters.

How the initiative plays out in the push and pull of Presidential politics will say less, perhaps, about campaign competitions and media preoccupations than about the general attitude of the American electorate toward the subject. When it comes to the dangers posed by nuclear arsenals, complacency reigns, even as the Trump Administration goes steadily about the business of opening up a new nuclear age. When Trump launched his “fire and fury like the world has never seen” tirade against North Korea, in August of 2017, there was a short-lived rush of nuclear anguish, with many people of a certain age recalling incidents of Cold War Armageddon dread. But, with Trump’s irrational about-face on North Korea, which seems based on what he has called the “love” between him and Kim Jong Un, and which his own intelligence chiefs discounted earlier this week, the broad fear of nuclear war resumed its place in the deep recesses of American denial.

Warren is not taking her cues on this question from the polls. If she were, she would, like most other politicians, likely leave it alone. For two generations, Americans have not known how to think about the nation’s nuclear policy, or its arsenal, and so, for the most part, it seems, they haven’t. The twenty-first century’s stalling of arms reduction, and the withering of the U.S. commitment to the arms-reduction-treaty regime, have ranked low on the scale of the nation’s problems, as perceived from across the political spectrum. Obama’s brief emergence as a globally celebrated nuclear eliminationist, and his inexorable fade from that stance when he was actually in power, says less about a leader’s fecklessness than about the deadly lock that nuclear weapons have had on one Congress after another, on the ever-burgeoning defense industry, and on the American mind.

There was an exception, which came during the fraught period of the first term of the Reagan Administration, when a burst of nuclear-war anxiety swept across much of the world. In Europe, the deployment of American cruise and Pershing II missiles ignited unprecedented grassroots protests. In this country, that anxiety inspired the Nuclear Freeze Movement—which called for a freeze on the super-powers’ nuclear arsenals at their then current levels—with municipalities, civic and professional groups, religious institutions, and cohorts of educators, physicians, and scientists all banding together against what felt like an imminent nuclear catastrophe. By March of 1982, the grassroots had sprouted a forest, and the nuclear-freeze resolution, “A Call to Halt the Nuclear Arms Race,” inspired a bill in Congress by sponsors that included two Massachusetts Democrats: Senator Ted Kennedy and Representative Ed Markey, who is now Warren’s colleague in the Senate. (Markey, with Representative Ted Lieu, of California, reintroduced a similar bill of his own this week) Three months later, a million anti-nuke protesters gathered in New York City. A year after that, the nuclear-freeze resolution passed in the House.

The idea of the freeze then opened into the larger idea of nuclear reduction, and, over time, to a wide embrace of the goal of nuclear abolition. Members of the Pentagon’s nuclear priesthood, including General Lee Butler and Admiral Eugene Carroll, Jr., and civilian architects of the nuclear-security state, such as Paul Nitze and William Perry, began to speak out against nukes. For a time, liberation from the grip of the absolute weapon seemed possible. Even Reagan had been preparing to move past the idea of freezing nuclear-arms levels to reducing them. Then, Mikhail Gorbachev became the leader of the Soviet Union, a historic shift occurred, and, against all predictions, the Cold War ended, not with conflagration but with negotiation. (On Friday, the Trump Administration suspended the Intermediate-Range Nuclear Forces Treaty, which came out of those negotiations, in 1987, following a long-running disagreement over Russia's compliance.)

“No first use” is a simple idea, as the freeze was, and that is its strength. It is common-sensical, and harkens back to the informal moral consensus that America is not a nation to start a nuclear war. That consensus should be enshrined in law, but, even if all that comes of the Smith-Warren initiative is a renewed public debate, that will be more than salutary. Consideration of the No First Use Act not only in Congress but on the campaign trail can point forward to a new grappling with the unexamined set of nuclear questions, starting with Warren’s other two core principles: of no to new weapons and yes to arms control. More than her proposals for the recovery from income inequality, her effort to unbolt the nuclear lock on the American economy and culture can be historic.