(CNN) White House officials are losing confidence that Ukraine will ever be able to take back all of the land it has lost to Russia over the past four months of war, US officials told CNN, even with the heavier and more sophisticated weaponry the US and its allies plan to send.
Advisers to President Joe Biden have begun debating internally how and whether Ukrainian President Volodymyr Zelensky should shift his definition of a Ukrainian "victory" -- adjusting for the possibility that his country has shrunk irreversibly.
US officials emphasized to CNN that this more pessimistic assessment does not mean the US plans to pressure Ukraine into making any formal territorial concessions to Russia in order to end the war. There is also hope that Ukrainian forces will be able to take back significant chunks of territory in a likely counteroffensive later this year.
A congressional aide familiar with the deliberations told CNN that a smaller Ukrainian state is not inevitable. "Whether Ukraine can take back these territories is in large part, if not entirely, a function of how much support we give them," the aide said. He noted that Ukraine has formally asked the US for a minimum of 48 multiple launch rocket systems, but to date has only been promised eight from the Pentagon.
And not everyone in the administration is as worried -- some believe Ukrainian forces could again defy expectations, as they did in the early days of the war when they repelled a Russian advance on the Ukrainian capital of Kyiv. National security adviser Jake Sullivan has remained highly engaged with his Ukrainian counterparts and spent hours on the phone last week discussing Ukrainian efforts to recapture territory with Ukraine's defense chief and Chairman of the Joint Chiefs of Staff Gen. Mark Milley, officials familiar with the call told CNN.
The growing pessimism comes as Biden is meeting with US allies in Europe, where he will try to convey strength and optimism about the trajectory of the war as he rallies leaders to stay committed to arming and supporting Ukraine amid the brutal fight.
"We have to stay together. Putin has been counting on from the beginning, that somehow NATO and the G7 would splinter, but we haven't and we're not going to," Biden said Sunday while at the G7 summit in the Bavarian Alps.
The administration announced another $450 million in security assistance to Ukraine last week, including additional rocket launch systems, artillery ammunition and patrol boats. The US is also expected to announce as soon as this week that it has purchased an advanced surface-to-air missile defense system, called a NASAMS, for Ukrainian forces. Biden indicated in an op-ed earlier this month that he is committed to helping Ukraine gain the upper hand on the battlefield so that it has leverage in negotiations with Russia.
The mood has shifted over the last several weeks, though, as Ukraine has struggled to repel Russia's advances in the Donbas and has suffered staggering troop losses, reaching as many as 100 soldiers per day. Ukrainian forces are also burning through their equipment and ammunition faster than the West can provide and train them on new, NATO-standard weapons systems.
A US military official and a source familiar with Western intelligence agreed it was unlikely that Ukraine would be able to mass the force necessary to reclaim all of the territory lost to Russia during the fighting -- especially this year, as Zelensky said on Monday was his goal. A substantial counteroffensive might be possible with more weapons and training, the sources said, but Russia may also have an opportunity to replenish its force in that time, so there are no guarantees.
"Much hinges on whether Ukraine can retake territory at least to February 23 lines," said Michael Kofman, a Russian military expert at the Center for Naval Analyses. "The prospect is there, but it's contingent. If Ukraine can get that far, then it can likely take the rest. But if it can't, then it may have to reconsider how best to attain victory."
Russian forces now control more than half of the eastern Ukrainian region of Donetsk, Pavlo Kyrylenko, the head of the Donetsk region military administration, said Thursday. Ukrainian forces retreated from the key eastern city of Severodonetsk on Friday after weeks of bloody battle.
Russian forces last week also captured ground around Lysychansk, the last city in the eastern Luhansk region still controlled by Ukraine. Ukrainian military commanders are now grappling with the reality that they may have to withdraw from the area to defend territory further west.
In the meantime, Russian oil revenues have only been going up as oil prices have skyrocketed, even amid the harsh sanctions imposed by the West. US officials said on Monday that the US and its allies are going to try capping the price of oil so Russia does not profit from it anymore, but how and when that cap will take effect remains to be seen.
Internally, there is a sense among some in the Biden administration that Zelensky will need to start moderating expectations for what Ukrainian forces can realistically achieve. Zelensky said late last month that he would "consider it a victory for our state, as of today, to advance to the February 24 line without unnecessary losses."
He reiterated that goal last week.
"We don't have any other choice left but to move forward -- move to liberate all of our territories," he said in a Telegram post. "We need to kick the invaders out of the Ukrainian regions. Though the width of the frontlines is as long as over 2,5000 km, we feel that we hold the strategic initiative."
And on Monday, he put a timeline on it: He wants the war over, and for Ukraine to win, by the end of 2022, he told G7 leaders.
Russia is suffering acute combat losses as well, losing as much as a third of its ground force in four months of war, US intelligence officials estimate. Officials have also said publicly that Russia will struggle to make any serious gains further west, using the Donbas region as a staging ground, without a full mobilization of its reserve forces.
But Russia believes it can maintain the fight, wearing down Ukrainian and western resolve as the global economic effects of the war become more severe, officials have told CNN.
As CNN has previously reported, Russia is looking in particular to exploit the gap between how much Soviet-style ammunition Ukraine and its allies have in their stockpiles, and how long it will take the west to provide Ukraine with modern, NATO-standard weapons and munitions that require time-consuming training.
A senior defense official acknowledged to CNN that the Soviet-era stocks are "dwindling," but haven't yet reached "rock bottom." The official said that some eastern European countries still have more they could provide -- but only if they continue to be backfilled by allies with more modern equipment.
The US and its allies, meanwhile, have been scrounging the world for the kind of Soviet-era ammunition that fits the equipment Ukraine already has, including 152 mm artillery ammunition. NATO-standard weapons fire larger, 155mm rounds. But another US defense official told CNN that effort is effectively reaching its end, with almost everything available that countries are willing to provide having already gone in.
Given the prodigious rate at which the Ukrainians have gone through their older ammunition in the bruising artillery fight in the Donbas, the official said, "Soviet-era weapons are being wiped off the earth."