Asked during a 2010 Editorial Board endorsement interview to identify a global threat that kept him up at night, U.S. Rep. Tim Walz pointed to Russia and nuclear security.

The Minnesota Democrat recently reminded an editorial writer of that conversation in light of recent events. Today, he has plenty of company. President Obama may not have focused his first campaign for the White House on global security, but once in office he made nuclear weapons a top foreign policy issue.

Since the first Nuclear Security Summit five years ago, there’s been progress. Thirteen nations have gotten rid of nuclear materials, and many more have improved security at nuclear storage facilities.

Another milestone occurred Monday, when Japan announced a plan to turn over to America more than 700 pounds of weapons-grade plutonium and a stockpile of highly enriched uranium. While there was no threat that Japan’s postwar constitution and political culture would lead to development of a nuclear weapons program, the announcement should reduce rising tensions between Japan and some of its Asian neighbors. At a minimum, the move will reduce the possibility that the weapons-grade materials might end up in rogue hands.

The announcement was made at the 2014 Nuclear Security Summit, which is being hosted at The Hague, Netherlands. But Moscow will clearly be on the minds of the participants as they discuss curbing global nuclear proliferation.

Russia plays a key role in ongoing negotiations involving Iran and North Korea. And Russian President Vladimir Putin just made those negotiations harder by annexing Crimea despite a guarantee that Ukraine’s territorial sovereignty would be respected in exchange for relinquishing its post-Soviet nuclear arsenal.

Putin’s increasingly bellicose disruption to the post-Cold War order was the top topic in a hastily arranged Group of 7 meeting Monday. Leaders from the United States, Great Britain, Canada, France, Italy, Germany and Japan are trying to coordinate an effective economic and diplomatic response to Russia’s aggression. A significant symbol is the meeting itself: It won’t be a G8 gathering, because Russia has been benched from the exclusive club of top economies.

Yet reflecting the challenge the United States and European Union face in responding to Russia, at the same time Russian participation is considered crucial for two other numerically named nuclear diplomacy efforts: The P5+1 (the five permanent members of the U.N. Security Council — United States, United Kingdom, France, Russia and China — plus Germany) talks regarding Iran’s potential nuclear weapons program, and the six-party talks (United States, Russia, China, Japan, South Korea and North Korea) on containing North Korea’s nukes.

Russia has hinted that Western sanctions may prompt the country to amend its cooperation in Iran negotiations. Moscow could threaten similar self-serving and self-destructive diplomacy regarding North Korea.

While the stakes of nuclear proliferation in Iran and North Korea carry more geopolitical gravity than control of the Crimean peninsula, they’re clearly linked. Western leaders would be making a grave mistake if they curb their response to the illegal annexation in Ukraine. The best method of achieving nuclear security is through the unified efforts of the international community. In fact, the only reason that Iran is at the negotiating table is because severe sanctions threatened the theocracy that rules the country. Letting Russia off the hook would embolden other rogue actors, which might increase the perceived need to develop a nuclear deterrence.

The current climate will indefinitely table talks between Russia and the United States on reducing nuclear arsenals. But Russia must not be allowed to thwart other efforts. It cannot use its role in nuclear negotiations as a shield for territorial aggression. A stalwart Western response to solidify Ukraine and punish Russia should also send a signal to states seeking or possessing nuclear weapons that the international community can effectively rally to deter them, too.