MUNICH — When President Joe Biden met with his European counterparts in March, the mood — despite the grim circumstances — was almost heady: A weeks-old Russian invasion of Ukraine had prompted a remarkable show of unity from the global community and an unexpected resolve from Ukrainian fighters on the battlefield.

But now, three months after those meetings in Brussels, Biden will arrive Saturday in the Bavarian Alps to begin a pair of summits that will confront a far more somber situation in Ukraine. Instead of celebrating a heroic rebuff of Russia, Biden and his fellow leaders will be wrestling with how to manage a slog.

The president is also departing the United States just a day after one of the most consequential Supreme Court decisions in history. The overturning of Roe v. Wade on Friday is roiling the country and animating the Democratic Party just as its leader leaves for a long-planned trip abroad.

The previous unity among Western nations is showing signs of fracturing, with splits emerging between those who favor a negotiated peace as soon as possible and those who want to let Ukraine fight as long as it takes to reclaim its territory. The war has meanwhile taken a punishing toll on the global economy, and rocketing gasoline prices back home will make it harder for leaders to impose even more sanctions on Russian oil.

What began as a nearly unprecedented display of transatlantic unity, with Ukrainian President Volodymyr Zelensky rallying the world’s democracies to stand by his country, has now evolved into a longer, more complex struggle, with no clear end in sight.

“Both the reality and the mood have shifted. Things are trending against Ukraine, trending toward Russia, given the nature of the battle at this point,” said Richard Haass, a veteran diplomat and president of the Council on Foreign Relations. “So the question is: What more are countries prepared to do to help Ukraine militarily and economically? But it’s a more sober and somber mood. The trends are not good.”

The financial cost of the conflict has sharply escalated four months in, both the money required for Ukraine to fend off Russia’s aggression and the toll on the global economy. When the leaders gather this coming week — first for a meeting of the Group of Seven industrialized nations in Germany, followed immediately by a NATO summit in Spain — the discussions will focus less on the lofty language of democracy and more on the hard realities of whether the allies can maintain their newfound unity.

“This is very different from his last summit,” said Ian Bremmer, president of the Eurasia Group, a global risk consultancy. “This is not a summit about deliverables, it’s not a summit about body language, it’s not a summit about a communique. It’s a summit about war, a summit about a global crisis that will dominate all the conversations.”

Bremmer added that NATO members will need to focus on the basic architecture of the alliance and questions that have not arisen since the Balkan wars of the 1990s. Already the Ukraine war has both strengthened NATO — Finland and Sweden are asking to join — and exposed its divisions, as Turkey splits with the other allies in objecting to the two countries’ candidacy.

“You’re expanding NATO, you’re spending more money on defense, you’re forward-deploying troops, and you’re in an environment where there’s going to be cyberattacks and espionage from Russia,” Bremmer said. “This is literally a new cold war, with elements of a hot war with Russia. And the question is, how are you going to deal with that?”

Zelensky will address the G-7 and NATO summits virtually, in an effort to prod Western nations to maintain the enthusiastic backing his country attracted in the war’s early stages.

But divisions are emerging over how much and what kind of military assistance to provide Ukraine. Countries face different levels of war fatigue and a dependence on Russian natural gas that varies by country. If the last gathering showcased a unified response, this one is overshadowed by questions of whether these disagreements can be resolved.

“The overarching theme for G-7 and NATO is the high political and economic costs of doing what is right versus doing what is easy,” said Heather Conley, president of the German Marshall Fund. “The Kremlin is banking that we won’t pay those costs. They’ve been wrong so far. But will they be wrong over the next six months when the pain is felt most acutely?”

Biden’s meetings start on Sunday at Schloss Elmau, Germany, where G-7 leaders will discuss the high prices and food and energy crises that have resulted from the war.

Biden is then scheduled to travel Tuesday to Madrid for the NATO summit, which is likely to include spirited discussions on whether to admit Finland and Sweden. The summit will also focus on efforts to integrate Ukraine into Europe’s basic alliances - NATO and the European Union a prospect that Russian President Vladimir Putin has signaled he would see as an existential threat.

“I think that’s very likely to happen,” Biden said this week of Ukraine joining the European Union. While E.U. membership can take years, getting the process underway would send a message and likely prompt a strong reaction from Russia.

Part of the European split over Ukraine is based on geography. Powerful countries like Britain, France and Germany are worried about the length of the war and the toll it may take as each faces domestic challenges, and may be more open to compromises that would bring the conflict to an end. Poland and the Baltic states, much nearer harm’s way, see any concessions to Putin as a dangerous reward for his brutality.

“The front-line countries to the east are the ones who see themselves in Ukraine’s shoes,” said Gideon Rose, a fellow at the Council on Foreign Relations. “They are worried about a future attack and are worried they would be the targets. The Eastern European countries are all in on helping Ukraine, because they understand this is the place to do it. If you let Russia get enough of a win that they don’t feel this was a mistake, not only will you not save Ukraine’s future, you also risk Russian thinking they can do this again.”

Early on, Biden was credited with mobilizing the international community in opposition to Russia’s invasion. He helped persuade allies to impose strict sanctions on Putin and his financial backers. International businesses have retreated from Russia, and the country has been isolated.

But as uncertainty replaces drama, the path forward is less clear.

“The oracle at Delphi could not predict to you the way this is going to end,” said Aaron David Miller, a veteran diplomat and senior fellow at the Carnegie Endowment for International Peace. “These meetings are extremely important to maintaining the effectiveness of the alliances for the next four or five months.”

In some ways, it is the alliance’s success in bolstering Ukraine that has made the war so unpredictable.

“There’s no prospect of either side winning, and virtually no credible prospect to lead to a compromise,” Miller said. “Tolstoy observed once that the warrior’s two greatest friends were time and patience. That’s the real problem that Biden’s Ukraine policy faces.”

The talks are also likely to include discussions of China’s economic power and Iran’s pursuit of a nuclear weapon.

In a call with reporters Wednesday, administration officials noted that, for the first time, the NATO gathering will include Asian leaders from Australia, Japan, New Zealand and South Korea — an addition the Biden officials cast as a sign that Russia’s invasion of Ukraine had “galvanized our partnerships around the world.”

“It’s also showing how Ukraine is not causing us to take our eye off the ball on China — in fact, I think quite the opposite,” a senior administration official said, speaking on the condition of anonymity under terms set for a call with reporters. “It’s firmed up the democratic world on both Russia and China, and President Biden has effectively linked our efforts in Europe and Asia.”

John Kirby, the National Security Council’s coordinator for strategic communications, said Thursday that one aim of Biden’s trip is to showcase his beliefs that NATO “truly has never been stronger and more viable than it is today” and that in person, face-to-face diplomacy is paramount. Biden is also hoping to win new commitments that will further isolate Russia from the global economy, Kirby said, and target the Russian defense supply chain.

“Instead of a shaken West,” he said, “we are more resolved than ever to support Ukraine and are leading that effort head-on at both the G-7 and the NATO summit.”

Max Bergmann, director of the Europe program at the Center for Strategic and International Studies, said NATO has a story of success to tell about the war in Ukraine so far — including Ukraine’s unexpected ability to withstand Russia’s aggression.

But, he added, as the leaders prepare to gather, “that initial triumphalism” is giving way to a more daunting reality: “The situation Ukraine finds itself now in is a long slog war of attrition against a global military superpower.”