Volodymyr Zelensky's visit to Washington sent Russia a message of steadfast unity and resolve, but defense analysts say he needs more concrete battlefield gains to sustain US and NATO backing through 2023 and fend off pressure to negotiate with Moscow.
In his first trip outside Ukraine since the war began last February, Zelensky earned firm pledges of support from President Joe Biden at the White House and then from US lawmakers whom he addressed in Congress.
That adds pressure on Kyiv's forces to show more progress in fighting Russia's army in the coming months.
"For the next several months, Ukraine is in a good spot in terms of financial support from both the United States and European allies and partners," said Luke Coffey, a defense expert at the Hudson Institute.
Sometime this winter Coffey expects Kyiv's forces to launch a new thrust toward Russian-held Melitopol in the south.
If successful, that could shore up support over the longer term, he said.
"But we have to start thinking like, this will be a war that's measured in years and not months. And we have to start planning accordingly," he added.
Washington's commitment was on display during Zelensky's lightning half-day visit.
Congress is near to approving $45 billion in aid for Ukraine, and the White House announced a new $1.85 billion arms package, including a Patriot missile battery, the Pentagon's most advanced air defense system.
But the White House continued to hold back on Ukraine's requests for more, like longer-range ATACMS missiles, advanced attack drones and F-16 fighter jets.
In explaining why in a joint press conference with Zelensky, Biden indicated fragility of allied support for the war.
"I've spent several hundred hours face-to-face with our European allies and the heads of state of those countries, and making the case as to why it was overwhelmingly in their interest that they continue to support Ukraine," he said
"They understand it fully, but they're not looking to go to war with Russia."
Michael Horowitz, head of intelligence at LeBeck International, a Middle East security consultant, said there are "unexpressed concerns" among allies over whether Zelensky's goal of retaking all of Ukraine, including Crimea, from Russia is achievable.
"As the Russian invasion stalls, Putin is counting on war fatigue, both inside and outside of Ukraine, to force Kyiv into settling," said Horowitz.
That is the goal of Russia's "winter strategy" of attacking Ukraine's electricity network and driving up food and fuel prices globally, he said.
"What Ukraine will need more than anything else in the coming months are new military victories. Those victories are the only effective way to truly stave off conflict fatigue," he said.
- 'Putin's forever war -
That could be difficult. Hudson's Coffey said both sides will score wins and losses in the coming campaign, and any offensive by Ukraine in the south could be complicated by a mainly diversionary Russian assault from the north.
"The problem is that we are not in 1944 or 1945," said Mykola Bielieskov, of Ukraine's National Institute for Strategic Studies, referring to the final years of World War II, when Germany's ultimate defeat was looming.
"It's more like the end of 1942/beginning of 1943. There is still way to go to ultimate triumph" over Russia, he wrote on Twitter.
Seth Jones of the Center for Strategic and International Studies in Washington said all indications from Moscow point to a "protracted war and willingness to spend whatever it takes."
On the same day Zelensky travelled to Washington, Putin met with his top military officials and announced plans to expand and better equip his armed forces.
"We don't have any limits on funding. The country and the government is giving everything that the army asks for, everything," Putin said.
"This is, every indication we have seen, Vladimir Putin's forever war," Jones said.