At the U.N. General Assembly meeting in September, President Obama presented his list of “new dangers” confronting the world: the Islamic State, Ebola and Russian aggression in Ukraine. He seemed not to be pulling his punches. “We believe that right makes might, that bigger nations should not be able to bully smaller ones and that people should be able to choose their own future,” Obama said.

But eight months later, Secretary of State John F. Kerry was on his way to Sochi, Russia, for a rare high-level meeting with President Vladi­mir Putin that focused on issues such as limiting Iran’s nuclear program and combating Islamist terrorism even as the Russian leader fanned the flames of crisis in eastern Ukraine. It was a mission that the administration had debated for months, with Obama and Vice President Biden fearing that it might be misinterpreted as an easing of the U.S. position on Ukraine.

The U.N. meeting and Kerry visit are bookends of an Obama policy on Russia that has bounced from cooperation to confrontation and eventually to compartmentalization.

The shifting strategies reflect a constant tension — between principle and pragmatism, isolation and engagement — that has made it so difficult for Obama to deal with Moscow on a series of issues without seeming to go soft on the Russia’s annexation of Ukraine’s Crimea region.

Those tensions come to a head this weekend in Germany, where Obama is attending a Group of Seven summit that will be consumed by Ukraine, the pending Iran nuclear deal, and the wars in Iraq and Syria. Each puts different demands on Obama’s relations with Putin. On the first, Obama needs to confront Putin; and, on the latter two, progress isn’t possible without, at least, tacit support from the Russian leader.

Russian President Vladimir Putin chairs a meeting of the Council for Interethnic Relations and the Council for the Russian Language at the Kremlin in Moscow, Russia, onTuesday, May 19, 2015. (Alexander Nemenov/ Pool photo via AP) (Alexander Nemenov/AP)

With the escalation of attacks last week by Russian-backed separatists on Ukrainian forces and the continued forward positioning of heavy artillery in violation of cease-fire agreements, Russia is leaving the G-7 leaders little choice. White House officials said that Obama would not only support existing sanctions but would also consider imposing more.

“It’s important for Russia to understand that, should it continue to have further escalation in Ukraine, it could be faced with additional consequences,” the deputy national security adviser, Ben Rhodes, said in a conference call with journalists Thursday.

The G-7 meeting is a symbolic moment. After the Cold War, the annual gathering of the leaders of the world’s major industrial nations had added Russia and went from being known as the G-7 to the G-8 — a gesture welcoming Moscow into the wider community of nations and a tribute to the “Bill and Boris show” that featured presidents Clinton and Yeltsin.

But when Putin seized Crimea last year, that violation of international borders set off alarms throughout Europe and in the United States. When the group of world leaders met in Belgium in last June, Putin was left out.

This weekend’s gathering will again revert to being the G-7, excluding Russia for only the second time in two decades. Yet, with renewed violence in eastern Ukraine, Moscow is ensuring that its absence will be palpable.

“We haven’t been concerned with security in Europe in 30 years. We thought this was done,” said Michael McFaul, Obama’s former ambassador to Russia, “and over the last year and a half we learned that’s not true.”

“We’re not back in the Cold War, but neither are we in the strategic partnership we have tried to establish,” said Jens Stoltenberg, secretary general of NATO.

People watch the anti-G-7 demonstration from their house in Garmisch-Partenkirchen, southern Germany Saturday. The G-7 two-day summit begins on Sunday. (Wolfgang Rattay/Reuters)

Aggressive Russian military maneuvers have galvanized Europeans, who Stoltenberg says must boost military spending. NATO — which will hold its summit next year in the Polish presidential palace’s Column Hall, where the Warsaw Pact binding the Soviet Union together with its Eastern European allies was signed in 1955 — has increased military activity in countries bordering Russia. On Friday, it began a 17-nation naval exercise in northern Europe’s Baltic Sea, and starting Tuesday in Poland, it will launch a 10-day deployment test for the alliance’s new quick-reaction force.

The United States is also rotating more forces through the Baltic states and Poland.

For the most part, though, what was an acute crisis last year has settled into a frozen conflict, at best, testing U.S. and European resolve to maintain — or toughen — economic sanctions. Russia has tried wooing the Czech president and the leaders of Hungary and Greece, but German Chancellor Angela Merkel has led the push for keeping costly sanctions in place as long as Russia fails to abide by the terms of the Minsk cease-fire agreement.

The crisis in Ukraine also has forced the Obama administration to reexamine its Russia policy that began six years ago with an optimistic “reset” and that has become one in which the two leaders no longer speak to each other.

For months, an interagency policy review has wrestled with issues such as whether Russia should be seen as a global or regional power and whether the United States should send lethal weapons to Ukraine. It also has grappled with how to compartmentalize topics such as Iran, terrorism and the Islamic State, on which the United States might choose to continue cooperating with Russia even as it confronts the country.

The Obama administration even struggled for weeks over how to describe the forces fighting the government in eastern Ukraine, a senior administration official said. In the end, the administration stopped calling them Russian-backed separatists and started calling them “combined Russian-separatist forces” — an effort to shame Russia publicly into changing its behavior rather than hoping to keep Russia’s direct involvement quiet and letting Putin choose a face-saving exit.

Obama shows little inclination to talk to Putin himself; even before the Ukraine crisis, Obama canceled a visit to Moscow in 2013 after Russia granted asylum to Edward Snowden, who revealed classified secrets about the National Security Agency’s far-reaching surveillance program.

But current and former White House officials say that Obama has been intimately engaged in U.S.-Russia relations. He helped negotiate details in the telemetry chapter of the Strategic Arms Reduction Treaty, or START, when Dmitry Medvedev was Russia’s president. Last fall, he disagreed with senior Democratic Party experts on Russia — including former deputy secretary of state Strobe Talbott, Biden and former national security adviser Zbigniew Brzezinski — who over dinner at the White House urged Obama to send lethal arms, such as antitank weapons, to Ukraine to raise the conflict’s cost to Russia.

A former administration official said that one of the questions he has heard Obama ask on issues including Ukraine was: If it’s not going to be effective, why do it?

That reasoning, along with Merkel’s agreement, has stiffened his determination not to send weapons to Ukraine. Doing so, he has said, would not be enough to defeat Russian and Russian-backed forces in Ukraine, and it would only risk escalating the fighting.

Moreover, Obama tends to see Russia in terms that he laid out in a news conference at The Hague in March 2014. He called it “a regional power that is threatening some of its immediate neighbors — not out of strength but out of weakness.”

But Obama also has come under criticism from some Russia experts who say that with that comment and others, he needlessly has antagonized Putin and overestimated the speed with which economic sanctions would, as Obama put it after last year’s G-7 meeting, give Putin “a chance to get back into a lane of international law.”

“I talked to a Russian acquaintance who said if we could get back to peaceful coexistence, that would be an improvement,” said Angela Stent, a Georgetown University professor and a former State Department and National Intelligence Council official. “Peaceful coexistence” is the phrase coined by Soviet leader Nikita Khrushchev in 1953 to reduce tensions among communist and capitalist blocs.

Russia has, even during the Ukraine crisis, continued to help identify and destroy Syria’s stockpiles of chemical weapons. But many Russia experts say that the Obama administration underestimated Putin’s determination to fuel the Ukraine conflict, even though it was not in Russia’s interest.

“He’s not a chess player — he plays checkers. That’s why we’re surprised. We thought he was playing chess,” said Derek Chollet, a former assistant secretary of defense for international security affairs who is now at the German Marshall Fund.

As the conflict in Ukraine drags on, the administration has been more ready to openly point to Russia’s direct participation.

“One other effective tool that we’ve seen quite recently is making clear that there are Russians operating in Ukraine and that some of those Russians are being killed,” Charles Kupchan, senior National Security Council director for European affairs, said in a conference call Thursday. “The presence of Russian troops in eastern Ukraine is something that the Russian government has tried to deny, but the more evidence and the more public evidence there is of that presence, the more pressure there is on Vladimir Putin.”

Taking the measure of Putin has been the real center of Russia policy. When Medvedev was president, the two countries agreed on a new START, U.N. resolutions on Iran and North Korea, membership in the World Trade Organization, new supply routes to U.S. troops in Afghanistan, and economic liberalization. “We were getting big stuff done,” said McFaul, the former ambassador.

But then Putin declared his candidacy to run for president again. And he condemned the U.S. and NATO air attacks on Libya, railed against what he called U.S. interference in his reelection bid and took issue with the notion of U.S. exceptionalism. Putin was particularly angered by McFaul’s efforts to encourage “civil society,” the people and groups independent of the government.

The last time that McFaul met Putin, during Kerry’s previous visit to Moscow two years ago, Putin told Kerry that the United States was naive to think it could foster Russian opposition groups. “He was pretty blunt about it. He looked right at me,” McFaul recalled. “He didn’t use my name but said, ‘We know what your embassy is doing here in its support for the opposition, and we don’t appreciate it.’ ”

Yet many Russia experts say that if naivete was involved, it was the belief that Putin, who invaded Georgia when George W. Bush was president, would not seek to keep other neighboring states in Moscow’s orbit.

At this point, experts say that Obama and his foreign policy team no longer hope for cooperation or democratic reform in Russia. “I think they’re more concerned about Russians doing mischief, rather than a positive contribution to what we’re trying to achieve,” said Thomas Graham, a managing director at Kissinger Associates who was NSC director for Russia under Bush. He cited the need to keep Russia in agreement with other powers for an Iran accord.

Beyond that, though, Graham added: “There are no expectations for the relationship. They just don’t want things to blow up between now and the end of the term.”