Biden heads to high-stakes NATO summit amid showdown with Putin over Ukraine

President Joe Biden headed to Europe Wednesday as he tries to keep NATO allies and other European partners united against Russian President Vladimir Putin and his invasion of Ukraine.

With fighting lasting nearly a month -- and Ukrainian forces unexpectedly holding Russia to a standoff -- Biden and other world leaders will seek to speed an end to the conflict.

They'll face pressure to make announcements about new sanctions on Russia, humanitarian assistance for refugees and additional support for Ukraine's military.

Putin and China will be watching, with the fate of Ukraine -- and Russia's place in the world -- hanging in the balance.

And while Biden will command much of the attention this week, his Ukrainian counterpart, Volodymyr Zelenskyy, also plans to speak to -- and potentially pressure -- Biden and other NATO leaders.

Whirlwind diplomacy on display

Biden will spend much of Wednesday traveling from Washington to Brussels, ahead of a whirlwind day of diplomacy in the Belgian capital the next day.

On Thursday, he plans to attend an extraordinary summit of all 30 NATO leaders, where he will discuss deterrence against Russia and "reaffirm our ironclad commitment to our NATO allies," according to the White House.

Biden will also participate in a pre-scheduled meeting of the European Council -- the political body of the European Union -- and meet with leaders of the Group of Seven, or G-7, major industrial nations.

Throughout the meetings, Biden hopes to achieve "continued coordination and a unified response" to Russia, the White House said.

Biden has made working in lockstep with Europe a top priority, at times holding back sanctions -- such as on Russian energy -- to maintain that show of unity.

He has also fastidiously tried to avoid a wider conflict, declining to send American troops to Ukraine or support a NATO-enforced no-fly zone over the country.

Whether he'll push allies to more directly confront Russia -- by committing more troops to the region, providing even more provocative military assistance to Ukraine or otherwise directly assisting Kyiv -- remains to be seen.

One challenge he may face Thursday, though, is responding to Zelenskyy's remarks to NATO leaders.

The Ukrainian leader has repeatedly commanded the world's attention with moving, sometimes blunt addresses to national and international bodies. His direct demands sometimes go beyond Biden and other leaders' comfort levels, and he has not held back from naming and shaming those who he does not believe are doing enough to support Ukraine.

New sanctions and aid expected

Most major global summits are associated with major announcements, or "deliverables," often the result of months of negotiations.

But in this case, "the main deliverable is the trip and its symbolism," Stephen Sestanovich, a Russia expert and former ambassador at the Council on Foreign Relations, said.

But Biden and other leaders are expected to announce a new "package of sanctions" on Russia, too, including "tightening the existing sanctions to crack down on evasion and to ensure robust enforcement," U.S. national security adviser Jake Sullivan said Tuesday.

"One of the key elements of that announcement will focus not just on adding new sanctions," Sullivan said, "but on ensuring that there is a joint effort to crack down on evasion, on sanctions-busting, on any attempt by any country to help Russia, basically, undermine, weaken or get around the sanctions."

The president also "will have the opportunity to coordinate on the next phase of military assistance to Ukraine," Sullivan said.

And Biden will speak with leaders about "longer-term adjustments to NATO force posture on the eastern flank," Sullivan said, referring to the United States and other NATO countries deploying additional troops to countries that border Russia, like Poland, Estonia, Lithuania and Latvia.

He will also announce a "joint action on enhancing European energy security and reducing Europe's dependence on Russian gas," Sullivan added, without elaborating.

Focus on millions of displaced Ukrainians, US troops

In Brussels, Biden "will announce further American contributions" to help the 3.5 million Ukrainians who have fled the country and for the millions more who have become internally displaced, according to Sullivan.

On Friday, the president will travel to Poland, where he'll "engage with U.S. troops" – he has deployed thousands there in response to the invasion – and on Saturday, meet with Polish President Andrzej Duda. Poland has taken in more than 2 million Ukrainian refugees.

"It is the right place for him to go to be able to see troops, to be able to see humanitarian experts, and to be able to meet with the frontline and very vulnerable allies," Sullivan said.

White House press secretary Jen Psaki said this week that there were "no plans" for Biden to travel into Ukraine and that the White House had "not explored that option."

Putin, China watching

Biden said Monday that "the one thing I'm confident, knowing Putin fairly well -- as well as, I guess, another leader could know one another -- is that he was counting on being able to split NATO. He never thought NATO would stay resolved -- stay totally, thoroughly united."

"And I can assure you," he told a group of chief executives, "NATO has never been stronger or more united in its entire history than it is today, in large part because of Vladimir Putin."

In fact, Russia's invasion has united NATO against it. And a month of crushing sanctions have crippled Russia's economy and largely isolated Putin.

Whether world leaders in Brussels decide to ramp up the pressure on Putin in a way that could further change Putin's calculus -- and bring an end to war, perhaps by offering him a clear off-ramp -- could determine the length and course of the conflict.

But it's not clear the decreasing number of options they have left could fundamentally sway Putin. Russian troops continue to pummel Ukrainian cities and kill civilians even as the Ukrainians have prevented them from claiming major wins and toppling the government in Kyiv.

And it's not clear what that off-ramp could be. "Putin's back is against the wall," Biden said Monday.

The White House has warned Russia may launch cyber-attacks on critical infrastructure in the U.S. Such an attack could come in the next several weeks, although not necessarily in direct response to Biden's trip, according to Tom Graham, an expert on Russia at the Council on Foreign Relations.

And China's President Xi Jinping will be watching, too. In a call last week, according to the White House, Biden warned him of the consequences of providing aid to Russia.

Sullivan told ABC News' Elizabeth Schulze on Tuesday that, since last week, the U.S. had "not seen" China provide military equipment to Russia, as it had feared China may do.

The degree to which Biden is able to get European leaders on board with potential punishments for China could also determine whether Xi decides to support Putin or stay out of the fight.