President Donald Trump made the final stop of his traveling circus through Europe on Monday, meeting with Russian President Vladimir Putin in Helsinki. Afterward, both men held a news conference that will live in infamy, featuring a U.S. president stubbornly refuting clear evidence of Russian interference in U.S. elections and a Russian president playing his American counterpoint like Ronaldo plays a soccer ball — while giving the president the ball to boot.

Perhaps the only development that could be interpreted as positive: Both men confirmed that they discussed nuclear dangers that threaten both nations. While the policies and actions of both presidents have — rightly — generated angry domestic and international opposition, they may have begun laying a new foundation for cooperation between Washington and Moscow on nuclear threat reduction, something only they can do.

This fragile reed will not be easy to sustain. In his preceding stops in Brussels and the United Kingdom, Trump's berating and insulting of German Chancellor Angela Merkel and British Prime Minister Theresa May — fomenting regime change in Berlin and London — followed by his charge that the European Union is a "foe" of the United States, was a big dividend for Putin and weakened Trump's hand. The corrosive impact on Western cohesion of unwisely undermining a strong NATO and a special relationship between the U.S. and U.K. — two pillars of U.S. security vis-à-vis Russia — may yet undermine progress on nuclear issues.

Moreover, while presidents have great latitude in foreign affairs, international agreements require bipartisan congressional support. That does not now exist and will be more difficult to build, in particular in the wake of Trump's partisan attacks on Democrats while standing next to — and up for — Putin in Helsinki. If Robert Mueller's investigation concludes that the Trump campaign cooperated with Moscow in attacking our 2016 election, it may prove impossible.

Nevertheless, the fact that Trump and Putin apparently agreed in Helsinki to a new dialogue on strategic stability focused on nuclear dangers that threaten both nations has the potential to garner support from America's allies and friends in Europe — and across party lines in Congress. In short: Consistent with the conclusion that a nuclear war cannot be won and must never be fought, it makes sense for Europe, and sense in Washington, to work with Moscow to reduce nuclear risks — and thereby reduce the costs of sustaining our increasingly expensive nuclear deterrent.

Extending the 2011 New START Treaty to 2026, as Putin confirmed was discussed, means that America's and Russia's strategic nuclear forces — the only existential threat to the survival of both nations — would continue to be regulated and verified. This predictability would provide confidence in both capitals, and time to consider next steps in limiting existing nuclear inventories and emerging new technologies. It is also a necessary first step to reducing the staggering costs of the Trump administration's planned nuclear modernization program — now well over a trillion dollars.

Addressing compliance issues involving the 1987 Intermediate-Range Nuclear Forces (INF) Treaty, also mentioned by Putin, may be an important step back from the precipice of redeploying nuclear weapons in Europe that would again threaten every capital between London and Moscow. Resolving the issues raised by Russian cruise missiles, and addressing Russia's INF concerns with U.S. actions, will not be easy. But stopping the drift toward the demise of INF, an agreement that was central to ending the Cold War, is a step forward.

Committing to renew discussions on strategic stability will hopefully facilitate a return to talks among uniformed military leaders in charge of U.S.-Russian nuclear forces, and multilateral crisis management dialogue throughout Europe. The decision by Washington and NATO to stop talking with Russia after its annexation of Crimea has raised the risk of military conflict in Europe sparked by an accident, mistake or miscalculation — the kinds of scenarios that can be prevented when nations remain engaged. There is a reason why "hotlines" are called "hot" — and they should not be cut.

A clear directive by the two presidents to work to increase decision time for leaders to reduce the risk of a false warning of a nuclear attack or a nuclear accident or miscalculation would enhance stability. Also including in these discussions the threat of a cyberintrusion to nuclear facilities, strategic warning systems and nuclear command and control — and developing clear rules of the road to reduce cyberrisks — is a must.

Finally, agreeing to work together to advance the goal of "denuclearization" of the Korean Peninsula is an area where Washington and Moscow's experience on nuclear arms control can be positively applied. U.S.-Russian cooperation in diluting the nuclear threat in Northeast Asia would be a valuable achievement; it could also lead to reduced tensions and increased cooperation in other areas.

Trump is not shy about using the personal pronoun "I" in describing his influence on world events. In the case of nuclear threat reduction, unavoidably there are actually two "I's" — Trump and Putin — who must be in focus if we are to avoid a nuclear catastrophe.

Steve Andreasen, the director for defense policy and arms control on the National Security Council staff from 1993 to 2001, is a national security consultant who teaches at the University of Minnesota's Humphrey School of Public Affairs.