As the first anniversary of Russia’s invasion of Ukraine nears, U.S. officials are telling Ukrainian leaders they face a critical moment to change the trajectory of the war, raising the pressure on Kyiv to make significant gains on the battlefield while weapons and aid from the United States and its allies are surging.

Despite promises to back Ukraine “as long as it takes,” Biden officials say recent aid packages from Congress and America’s allies represent Kyiv’s best chance to decisively change the course of the war. Many conservatives in the Republican-led House have vowed to pull back support, and Europe’s long-term appetite for funding the war effort remains unclear.

Several officials noted the strong bipartisan support that has accompanied every Ukraine package, adding that Congress gave the White House more than it asked for, but they acknowledged that was under a Democrat-led House and Senate.

“We will continue to try to impress upon them that we can’t do anything and everything forever,” said one senior administration official, referring to Ukraine’s leaders. The official, who spoke on the condition of anonymity to discuss sensitive diplomatic matters, added that it was the administration’s “very strong view” that it will be hard to keep getting the same level of security and economic assistance from Congress.

“’As long as it takes’ pertains to the amount of conflict,” the official added. “It doesn’t pertain to the amount of assistance.”

The war in recent months has become a slow grind in eastern Ukraine, with neither side gaining the upper hand. Biden officials believe the critical juncture will come this spring, when Russia is expected to launch an offensive and Ukraine mounts a counteroffensive in an effort to reclaim lost territory.

Underlining the importance of the moment for the administration, Vice President Harris, Secretary of State Antony Blinken and Homeland Security Secretary Alejandro Mayorkas are heading to a major security summit in Germany this week and President Biden is traveling to Poland next week for a speech and meetings on the first anniversary.

The Biden administration is also working with Congress to approve another $10 billion in direct budget assistance to Kyiv and is expected to announce another large military assistance package in the next week and the imposition of more sanctions on the Kremlin around the same time.

The critical nature of the next few months has already been conveyed to Kyiv in blunt terms by top Biden officials — including deputy national security adviser Jon Finer, deputy secretary of state Wendy Sherman and undersecretary of defense Colin Kahl, all of whom visited Ukraine last month.

CIA Director William J. Burns traveled to the country one week ahead of those officials, where he briefed Ukrainian President Volodymyr Zelensky on his expectations for what Russia is planning militarily in the coming months and emphasized the urgency of the moment.

At the same time, Biden and his aides are eager to avoid any sign of defection or weakening resolve by Western allies ahead of the Feb. 24 anniversary, hoping to signal to Russian President Vladimir Putin that support for Ukraine is not waning.

But some analysts warned that neither Russia nor Ukraine is likely to seize a decisive military advantage in the foreseeable future.

“It feels like we are playing for a long war,” said Andrea Kendall-Taylor, director of the Transatlantic Security Program at the Center for a New American Security. “I think it’s at odds with what so many people would hope for, that we’re actually trying to help Ukraine win militarily.”

She added, “It feels like a moment of really high uncertainty.”

Biden and his top aides say they are determined to back Ukraine as long and as fully as possible. But they warn that the political path will get tougher once Ukraine has exhausted the current congressional package, which could happen as early as this summer.

Some Western leaders have harbored reservations about sending certain types of heavy weaponry to Ukraine, worried about a direct confrontation with Russia, especially after Putin signaled a willingness to use nuclear weapons.

But loud public lobbying by Zelensky, followed by quiet behind-the-scenes dealmaking by U.S. officials, has changed the dynamic. Biden and Blinken spent much of December and January working to convince allies to help provide Ukraine with the tanks and missiles that his administration had resisted sending for months.

Biden aides encouraged the Netherlands, for example, to help the United States provide critical air defense systems. On Dec. 20, officials at the National Security Council met with senior Dutch officials and stressed the importance the United States was placing on air defense, according to a senior administration official familiar with the meeting, who spoke on the condition of anonymity to reveal details of private discussions.

What the officials did not know was that the United States was working to bring Zelensky to Washington the next day, where Biden would announce that he was approving a Patriot Missile battery, Zelensky’s top request to help defend against Russian attacks on civilian infrastructure.

The battery needed a launcher — ideally one already in Europe — so Dutch officials worked through the holidays to see how they could assist the United States, the official said. In January, Biden invited the Dutch prime minister, Mark Rutte, to visit the White House, and the Dutch came up with a solution. When Rutte visited on Jan. 17, he said the Netherlands would provide two Patriot Missile launchers and missiles to Ukraine.

But Biden faced challenges on other fronts as well. While Britain had announced it would supply tanks to Ukraine, Germany refused to send its own Leopard 2 tanks or to authorize other countries to transfer their own Leopards — unless the United States agreed to send its prized M1 Abrams tanks to Ukraine.

For much of January, Pentagon and White House officials insisted the M1 Abrams tanks were not well-suited for Ukrainian troops because they are so complicated to operate and maintain. But Biden wanted to avoid the appearance of a fissure in the Western alliance.

In late January, Biden’s Cabinet came up with a plan for the United States to announce the provision of M1 Abrams tanks, which would placate Germany even though the U.S. tanks would not arrive for several months at the earliest. The following the day, Biden gave the go-ahead.

Now, as the United States prepares to send 31 of the premier tanks in the medium term, Europe is quickly assembling two Leopard tank battalions in the near term — the equivalent of at least 70 tanks — in a move that could significantly shift the balance of power on the battlefield.

Yet the public show of unity belies underlying tensions over how Ukraine should focus its resources in the coming months.

The frank discussions in Kyiv last month reflected an effort by the Biden administration to bring Ukraine’s goals in line with what the West can sustain as the war approaches its one-year mark. Getting Ukraine on the same page has not always been easy, according to people familiar with the discussions, speaking on the condition of anonymity to describe private talks.

For months, Ukraine has expended significant resources and troops defending Bakhmut in the eastern Donbas region. American military analysts and planners have argued that it is unrealistic to simultaneously defend Bakhmut and launch a spring counteroffensive to retake what the United States views as more critical territory.

Zelensky, however, attaches symbolic importance to Bakhmut, two senior administration officials said, and believes it would be a blow to Ukrainian morale to lose the city. On Friday, Zelensky said his country’s forces would “fight as long as we can” to hold the embattled city that Russia is on the brink of capturing.

While U.S. officials said they respect that Zelensky knows how best to rally his country, they have expressed concerns that if Ukraine keeps fighting everywhere Russia sends troops, it will work to Moscow’s advantage. Instead, they have urged Ukraine to prioritize the timing and execution of the spring counteroffensive, particularly as the United States and Europe train Ukrainian fighters on some of the more complex weaponry making its way to the battlefield.

“Generally, our view is they should take enough time that they can benefit from what we’ve provided in material and training,” a senior administration official said. If Russia takes Bakhmut, the official said, it “will not result in any significant strategic shift in the battlefield. Russians will try to claim it as such, [but] it’s a dot on the map for which they have expended an extraordinary amount of blood and treasure.”

Beyond Bakhmut, Zelensky has repeatedly rallied his country behind a military campaign to retake all of Russian-occupied Ukraine, including Crimea, the peninsula that Russia annexed in 2014.

Last month, Zelensky’s top aide, Andriy Yermak, reiterated that victory against Russia means restoring Ukraine’s internationally recognized borders, “including Donbas and Crimea.” Anything less is “absolutely unacceptable,” he said at the World Economic Forum in Davos.

U.S. intelligence officials have concluded, however, that retaking the heavily fortified peninsula is beyond the capability of Ukraine’s army right now, according to officials familiar with the matter, speaking on the condition of anonymity to discuss sensitive issues. That sobering assessment has been reiterated to multiple committees on Capitol Hill over the last several weeks.

That discrepancy between aims and capabilities has raised concerns in Europe that the Ukraine conflict will persist indefinitely, overburdening the West as it grapples with other challenges including stubbornly high inflation and unstable energy prices.

Against that backdrop, Biden’s aides say they are pursuing the best course of action: empowering Ukraine to retake as much territory as possible in coming months before sitting down with Putin at the negotiating table.

That effort will benefit from an influx of Patriot missiles, HIMARS launchers and an array of armored vehicles. Optimists see a path for Ukraine to stave off further Russian incursions in the east, retake territory in the south and force Russia to negotiate an end to the war by year’s end.

But skeptics worry that time is not on Ukraine’s side as Russia throws hundreds of thousands of new troops onto the battlefield, including convicts, in advance of the expected spring offensive.

Western and Ukrainian intelligence officials estimate that Russia has forces surpassing 300,000 in Ukraine, up from 150,000 initially, with plans to add hundreds of thousands more. The Russian campaign in the spring could see forces pouring over the Belarusian border and cutting off supply lines in western Ukraine that Kyiv has used to bolster its military.

Even seasoned military experts see a wide range of possible outcomes in coming months, underscoring how tenuous the situation is.

“It’s not clear how this ends. Will it end with a negotiated settlement? Will it just be protracted and we’ll see some version of the frozen conflicts we see elsewhere?” said Seth Jones, director of the International Security Program at the Center for Strategic and International Studies.

“You have sufficient support now and the Ukrainians are willing to fight, so there’s strong logic to getting Ukraine as much as you can,” Jones said. “How long you can continue to do that for is an open question.”

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