A Russian Yars RS-24 intercontinental ballistic missile system at a military parade in Moscow in May 2017. (Natalia Kolesnikova/AFP/Getty Images)

Jon Wolfsthal is Director of the Nuclear Crisis Group and a former Senior Director at the National Security Council. Michael McFaul is director of the Freeman Spogli Institute for International Studies and a Hoover fellow at Stanford University, and a contributing columnist to The Post. He was previously special assistant to President Barack Obama at the National Security Council from 2009 to 2012, and a former U.S. ambassador to Russia from 2012 to 2014.

Vladimir Putin is no friend of the United States. The Russian president seeks to undermine many core interests of the United States, our allies, and our partners. In 2014, Putin annexed territory in Europe, seizing control of Crimea, and then intervened in eastern Ukraine, sparking a war during which more than 10,000 people have died. In 2015, Putin intervened militarily in Syria to prop up one of the most ruthless dictators in the world, and protects Bashar al-Assad’s rule even in the face of repeated use of outlawed chemical weapons. And in 2016, Putin violated American sovereignty by stealing data and spreading propaganda to influence our presidential election. Tragically but necessarily, the United States and our allies must seek to develop more effective strategies for containing Russian aggression, just as we did during the Cold War.

Yet despite all this, we must continue to manage our nuclear competition and shape the strategic nuclear landscape with Russia through tough, principled and effective arms control – again, just as we did during the Cold War. Presently, both the United States and Russia have met their obligations under the New START arms reductions treaty signed by President Barack Obama and Russia’s Dmitry Medvedev in 2010. In meeting this treaty obligation, the United States and Russia have reduced both the number of deployed nuclear warheads and delivery vehicles — with each permitted no more than 1,550 strategically deployed offensive nuclear weapons and 700 launchers for those weapons. This represents the lowest level of nuclear forces in both countries since President Dwight D. Eisenhower sat in the Oval Office.

Even as we mark this success, we are reminded that New START’s provisions don’t last forever. The 10-year agreement, which went into effect on Feb. 5, 2011, will expire in 2021. The Trump administration’s aversion to anything negotiated by the Obama administration, combined with legitimate concern over Russia’s violation of the Intermediate-Range Nuclear Forces Treaty, or INF, has halted any serious dialogue about arms control.

That’s a mistake. The lessons of the Cold War are that nuclear wars must not be fought and that arms races cannot be won. Of course, we must preserve a strong and effective nuclear deterrent to protect us and our allies. The United States’s nuclear forces and planned modernization are already more than capable of sustaining that deterrent for decades. But arms control agreements, such as the New START treaty, also advance U.S. security interests.

Consider the details: On-site inspections provisions have enabled both Russian and American inspectors to see that obligations have been met and that threats have been reduced. Each side has carried out more than 100 such inspections, and exchanged thousands of pages of information about current and future missile systems. New START gives us invaluable and irreplaceable information about Russia’s nuclear arsenal, and provides insight into their future capabilities. Our implementation of this treaty also helps demonstrate our continued commitment to nuclear reductions and leadership in the global nonproliferation effort. We have achieved these nonproliferation goals with no reduction in our own security, or in our ironclad commitment to our allies and theirs.

Reductions in our nuclear arsenals, a robust inspection regime, and efforts towards our global commitments to reduce nuclear weapons serve American national interests. Despite serious tensions over other security and economic issues, the United States and Russia have continued to implement this treaty not because of altruism, friendship, or third-party enforcement, but because of mutual self-interest. A self-enforcing agreement in the service of American security objectives is the hallmark of a successful arms control agreement.

In 2013, Russia refused offers to pursue deeper nuclear reductions and insisted that any future agreement also should address missile defenses, precision conventional weapons, and even conventional forces in Europe. Others have argued that the next round of nuclear arms reductions must include other nuclear powers. While addressing this complicated set of issues in new treaty negotiations is hard to envision in today’s environment, the same was true in the 1960s, 1970s, and 1980s, when America faced an even more intractable and threatening Soviet Union.

Instead of shying away from such broader discussions, Washington should welcome them. The government should expand the agenda to include our concerns about Russia’s vast stockpile of tactical nuclear weapons, new delivery vehicles such as long-range, nuclear-armed torpedoes, and violations of other agreements.

We cannot predict whether new arms-control talks will produce results, let alone what the next arms-control agreement might look like. But we know what happens when we lack the predictability and transparency that verified treaties provide. And we know that the next deal will not happen without direct negotiation with our Russian counterparts. We can contain Russia in some spheres, push back against its destructive behavior, promote democratic values and human rights, and still engage with the Russian government on nuclear stability and arms control. We successfully pursued this complicated strategy during the Cold War. We can do so again.

So let’s celebrate this terrific milestone of the current treaty today, but also begin work tomorrow to extend and strengthen arms control agreements with Russia in the future, not as a favor to Putin, but as a policy to enhance our security. The time to begin negotiating the next major arms-reduction agreement is now.