KYIV, Ukraine — As the Kremlin reveled in the failure of Congress to approve new military assistance for Ukraine and President Joe Biden railed against Republican lawmakers for “kneecapping” an ally in its hour of need, Ukrainian soldiers, political leaders and Ukraine’s allies were all left asking the same question Thursday: What happens if the United States stops providing military assistance?

Officials in President Volodymyr Zelenskyy’s government and Ukrainians themselves are still hopeful Congress will ultimately pass an assistance package — and have been cautious about saying anything that could ensnare them in America’s bitter domestic political battles.

But given the dire consequences if the United States cannot find a way to keep providing military assistance, officials in Kyiv are racing to bolster their nation’s own military capabilities and working to deepen ties with other allies who remain steadfast in their support.

“We will not stop defending our country — we will not give up a single piece of our land,” Oleksiy Danilov, the head of the Ukrainian National Security and Defense Council, said in a statement Thursday morning, hours after Republicans in the Senate blocked a measure to provide tens of billions of dollars more in aid to Ukraine.

“We will focus, draw conclusions, reload our weapons and continue to destroy the Russian monster,” he added.

The goal now, he said, was to make the nation’s military so strong that Ukrainians would not be “hostages to a changing political situation.”

Still, the uncertain prospects for more weaponry will reverberate on the battlefield, said Michael Kofman, a senior fellow in the Russia and Eurasia program at the Carnegie Endowment for International Peace. “U.S. military assistance to Ukraine is now running on fumes, and it is reflected by a tangible deficit of munitions at the front,” he said Thursday.

A shortfall in funding could quickly compromise Ukraine’s air defense capabilities, Jake Sullivan, the White House national security adviser, said in an interview. Western and Ukrainian officials have credited those systems with saving countless civilian lives as the Kremlin has repeatedly targeted population centers over the past two years.

At the same time, Sullivan said, the supply of 155 mm artillery rounds — essential in the brutal fight along the front — would rapidly decrease.

“That will mean Ukraine’s ability to defend against advanced Russian attacks that are happening right now, and Ukraine’s capacity to take more territory, will be severely degraded,” he said.

He added that the United States would no longer be able to send Ukraine air defense systems, such as Patriot batteries and missiles that are estimated to cost $1 billion each.

“And so Ukraine’s capacity to intercept missiles and drones and rockets being fired to destroy civilian infrastructure, as well as to attack its military, will be severely degraded,” he said.