Russian President Vladimir Putin’s nuclear saber-rattling and military brinksmanship have upended the rules that long governed relations between Moscow and Washington, presenting the United States with a dangerous dilemma.

The next U.S. president will inherit an increasingly fraught relationship with Russia in which Washington’s attempts to deter Putin have mostly failed. Moscow’s decision this month to pull out of a landmark agreement on disposing tons of weapons-grade plutonium, coupled with reports last week that Russia deployed new nuclear-capable missiles to Kaliningrad on the Baltic Sea, underscore how Putin is flexing Russia’s power in new and often unpredictable ways.

U.S. and European officials are increasingly alarmed over Putin’s willingness to risk military confrontation and threaten to use his country’s nuclear arsenal over issues the West sees as unrelated and separate. That makes it devilishly difficult for the United States and its European allies to find an effective response to Putin’s audacious tactics that in recent years range from Russia’s annexation of Crimea, to its air war in support of the Syrian regime, to Moscow’s suspected hacking of America’s presidential election.

“It very much feels like we are entering a very troubled and dangerous phase in this bilateral relationship,“ said Julianne Smith, a former senior Pentagon official who oversaw NATO policy and a former senior advisor to Vice President Joe Biden. “The next president will face some big strategic choices,” said Smith, who now advises Democratic presidential candidate Hillary Clinton on Europe and Russia.

President Barack Obama’s successor will have to choose from a range of unpleasant and risky options when it comes to handling a resurgent Russia, current and former officials said. A more conciliatory stance, aimed at cutting a grand bargain with Russia focused on Ukraine, would defuse tensions in the short term but at the cost of ultimately emboldening Putin. A more hawkish line — like the one championed by Clinton, who is leading nationwide polls — would risk escalation, with the chance of a military showdown in Syria or the Baltics.

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Following the failure of the Obama administration’s bid to “reset” policy with the Kremlin and capped by Putin’s return to the presidency in 2012, Russia has increasingly insisted on linking disparate issues, refusing to cooperate even on areas of common interest in order to pressure Washington on other disputes. That’s the opposite of how things worked in the era of superpower detente in the 1970s, when both countries obeyed clear boundaries and unwritten rules. Decisions on nuclear weapons, in particular, were kept apart from other issues and disputes around the globe.

The Kremlin jettisoned that approach after its annexation of Crimea in 2014 and its intervention in Syria in 2015, marking a definitive departure for Moscow and Washington, which had managed to wall off areas of disagreement from arms control cooperation.

In the Kremlin’s decree this month declaring Russia would no longer cooperate with the United States on a 2009 agreement to dispose of weapons-grade plutonium, Moscow said it would consider reviving the agreement only if the United States scaled back its military presence near Russia’s border, lifted all sanctions against Russia, and paid Moscow compensation for the economic losses caused by the sanctions.

U.S. officials said they were disappointed by Moscow’s decision and dismayed at what they consider a worrisome pattern of behavior.

The reports of the Iskander missile deployment to the Baltic enclave of Kaliningrad “represent the latest in a series of announcements and actions from Russia that call into question Russia’s commitment to minimizing the world’s most dangerous nuclear materials, and undermine the long path toward disarmament,” a senior administration official told Foreign Policy.

Russia in recent years has adopted a more aggressive doctrine on nuclear weapons, expanding the scenarios in which the arsenal could be used and employing threatening language when referring to its nuclear force. While running for election in 2012, Putin elevated the role of nuclear weapons in Russia’s strategic doctrine in an op-ed for the state-run Rossiyskaya Gazeta newspaper, even implying that they could be used in a conventional war. After taking office again as president, Putin announced a plan to modernize all three legs of Russia’s strategic nuclear forces.

In March, Putin said he had been ready to place nuclear forces on alert over the fate of the Crimean peninsula in Ukraine. Asked if Russia was prepared to bring its nuclear weapons into the conflict, Putin told state television: “We were ready to do it. I talked with colleagues and told them that this (Crimea) is our historic territory. Russian people live there, they are in danger, we cannot leave them.”

The United States says Russia has flouted a 1987 arms control treaty, negotiated by then-U.S. President Ronald Reagan and Soviet leader Mikhail Gorbachev, which called for the elimination of all ground-launched ballistic and cruise missiles with ranges of 500 to 5,500 kilometers. The treaty helped bring an end to the Cold War and served as a crucial foundation for arms control efforts.

After signing the New START arms control accord in 2010, Russia has rebuffed overtures from Obama during the past six years to negotiate further reductions in nuclear weapons. The treaty expires in 2021, and without a new deal, the gains in arms control over the last 25 years would be endangered. Putin’s government also has backed away from mutual efforts launched in the 1990s to secure nuclear material. In March, Russia declined to attend the Nuclear Security Summit in Washington.

Moscow is coupling that harsher atomic rhetoric with an increasingly aggressive maneuvering of its conventional forces. Russia has repeatedly sent its fighter jets and nuclear-capable bombers to skirt the boundaries of NATO and U.S. airspace since the Ukraine crisis and buzzed American planes and warships at close range. Russian planes have also routinely breached the airspace of non-NATO countries such as Finland and Sweden that joined the European Union’s sanctions against Moscow. In March 2015, Russia’s ambassador in Copenhagen said Danish warships would be “targets for Russian nuclear missiles” if they installed advanced radar equipment.

While the United States and NATO allies portray Russia as a provocative actor on the world stage, Moscow accuses the United States of fomenting “coups” in its backyard by supporting pro-democracy movements and destabilizing the nuclear balance with missile defense weaponry.

The United States for its part, withdrew from the Anti-Ballistic Missile Treaty in 2002. Russian officials have called the deployment of U.S. missile defense systems in Eastern Europe provocative and blamed the weaponry for derailing arms control talks.

Moscow has accused NATO and the United States of behaving recklessly, citing the deployment of more U.S. tanks and troops to NATO states bordering Russia and the use of B-2 bombers in drills close to the Russian border.

Searching for a way to manage relations, the Obama administration has opted to steer a middle course between confrontation and compromise, arguing that deterring Russia requires strategic patience. Economic sanctions, not arms, were the weapon of choice after the Ukraine invasion and Crimean annexation, for example. But sanctions, which have divided Europe and carry a cost, haven’t pushed out Russia’s “little green men” or restored Crimea to Ukraine.

“We have to come up with a coherent policy on Russia,” one Western diplomat said.

Against the sharp deterioration in U.S.-Russian relations, finding a new way to moderate mounting tensions between the two countries will be left to the next U.S. administration. In Syria, Russia’s deployment of fighter aircraft squadrons and artillery in 2015 blindsided the Obama administration, and has succeeded in shifting the tide of the war in favor of Syrian President Bashar al-Assad’s regime. The intervention has enabled Russia to set the agenda in Syria, reducing Washington’s influence and drastically limiting U.S. options for any military action.

When lawmakers last month asked the chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, about the possibility of the United States setting up a no-fly zone in Syria, he said it “would require us to go to war with Syria and Russia.”

Throughout her campaign, Clinton has repeatedly called for a no-fly or “safe zone” for Syrian civilians, without providing a detailed explanation as to what that would entail. But her advisors have suggested that it could involve the United States shooting down Syrian aircraft, forcing Russia to choose between defending Assad or working with Washington. In discussing the no-fly-zone idea, Clinton has not acknowledged the presence of an advanced Russian S-400 air defense system in Syria, which potentially could be used against U.S. aircraft enforcing a no-fly zone.

The Kremlin probably would view the prospect of a no-fly zone as a direct threat to its forces in Syria, particularly given how events unfolded in Libya when Clinton was secretary of state. In 2011, then-President Dmitry Medvedev had Russia abstain from a U.N. Security Council vote backing a no-fly zone in Libya. Clinton reportedly assured Moscow that the operation did not intend to bring about regime change in Libya and overthrow President Muammar al-Qaddafi. However, after NATO airpower allowed Libyan rebels to make gains on the ground and video emerged of Clinton joking, “We came, we saw, he died,” about the death of Qaddafi, the Kremlin believed it was deceived by the Americans. Experts say the intervention and Qaddafi’s death drove Putin to seek a return to the presidency.

In contrast with Clinton’s tough talk against Putin on the campaign trail, Republican presidential candidate Donald Trump has struck a friendly tone on Russia. His opponent has questioned his business ties to Russian investors and accused his aides of parroting Moscow’s propaganda. In a commentary published Thursday in the pro-Russian Sputnik website, Trump’s former foreign policy advisor, Carter Page, criticized the United States for “interference” in the domestic affairs of countries neighboring Russia, including Ukraine, and that Washington had shown a “complete disregard for Russia’s interests.” Trump has repeatedly called for closer cooperation with the Kremlin in combating the Islamic State in Syria, but otherwise has offered few specifics about how he would handle Russia. However, Trump’s campaign is imploding in the wake of sexual-assault allegations and Clinton is increasingly seen as the likely victor.

The Democratic nominee would bring her experience as secretary of state, four years that left her wary of Putin and skeptical that Moscow could be persuaded by diplomatic overtures or concessions. The Kremlin similarly views a Clinton presidency with apprehension over the hawkish policy positions she has outlined in Syria and Ukraine. But it remains unclear how far Clinton would be willing to go when it comes to asserting U.S. resolve and pushing back against Russia’s aggressive tactics, especially given Moscow’s willingness to link the conflicts to the wider issue of nuclear security.

Some of the current challenges carry echoes of the 1970s. Then, however, the two sides had a common understanding that circumscribed their competition. According to Henry Kissinger, the architect of detente under presidents Richard Nixon and Gerald Ford, “a conception of strategic stability developed that the two countries could implement even as their rivalry continued in other areas.”

That “strategic stability” — and the equilibrium it brought — unraveled with the demise of the Soviet Union. Russia felt threatened and humiliated by the expansion of NATO and the European Union to Central and Eastern Europe. It also was outraged by U.S.-led military interventions in Serbia and later in Iraq — without full authorization from the U.N. Security Council.

Experts on Russia disagree about how to handle Putin, and no Western government appears to have a clear idea as to how the former KGB agent would respond to different attempts at deterrence, or in what direction he intends to lead his country.

“We can see the tactics he’s using, and how he’s inserting himself in various global crises,” Smith said. “We’re not sure how far he wants to take this.”

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