A Ukrainian solider rushes through the front-line in Klishchiivka, eastern Ukraine, as gun and artillery fire erupt around him. Armed with an American-made M16 rifle, he and his unit storm an area that moments before was held by Russian forces.

Panting heavily as he dashes through the desolate landscape, he turns to a colleague holding a Belgian-made FN Minimi, ordering: "You, with the machine gun, hold this position."

The scene, recorded on the soldier's helmet camera, illustrates Ukraine's heavy reliance on international military support — especially on the equipment arriving from the United States — not just expensive body armor and high-tech missiles, but also small arms such as assault rifles and machine guns.

It also shows why the US Congress decision to pass a stopgap funding bill to avert a government shutdown, without additional funding for Ukraine, rang alarm bells from Kyiv right down to the front line.

US President Joe Biden was quick to try to reassure Ukraine and US allies that American support is unwavering, and called on Congress to follow through on a commitment to hold a separate vote on funding for Ukraine. But the damage was done: the squabble in Washington was a wake-up call for Ukrainians, indicating that US support could shift with the political winds in DC.

In Ukraine's east, where Ukrainian soldiers are waging a counteroffensive against Russian forces assisted by American weapons, that scenario is unfathomable.

Unfazed by the artillery duels just a few miles away, over the battered city of Bakhmut, Vasyl, 44, practices with a US-made M2 Browning machine gun. He scopes out targets in the training ground, carefully aiming before pressing the trigger.

"This is a large-caliber machine gun that works without failures," said Vasyl, who asked that his last name not be used due to safety concerns. "It's very handy when you are working from a high-rise, for example. You have the high ground and you see the enemy below."

Vasyl is part of the 80th airborne assault brigade's fire support team, providing units with cover while they advance and slow Russian forces when they counterattack. He said he can't imagine what would happen if Ukraine were to lose support from the US.

"I don't know what to say," he said. "That would be tough."

Hundreds of miles away, in the Ukrainian capital Kyiv, the government has downplayed the decision by Congress, billing it as a temporary halt and expressing confidence in American lawmakers approving continued military support for Ukraine.

In a wide-ranging interview with CNN, Ukraine's National Security Adviser Oleksiy Danilov said that the world was at a crossroads and that the US, as a guarantor of democracy globally, couldn't simply watch from the sidelines while his country continued to suffer under Russian aggression.

"It would be a great joy for [Russian President Vladimir] Putin and not only him, but for all autocratic regimes, if the US withdrew the assistance it provides to our country," he said. "Darkness can quickly engulf many countries... The American people need to choose - either the side of light or prepare for very unexpected events that may occur."

Danilov drew a historical comparison with the 1930s, "when everyone once turned a blind eye to Hitler's actions," but said he believed the US would remain committed to supporting Ukraine, saying he was sure the American people, including members of Congress, were "on the side of light."

"Regarding the (possible) end of the US support, we are more than confident that this will not happen," he added.

Back at the Ukrainian military training ground, smoke billows on the horizon but a momentary silence suggests an end to the artillery duel in the distance. It's short-lived. Seconds later, a rumble signals the firing of multiple-rocket launch systems, indicating this remains a very active frontline.

Vasyl is unperturbed as he reloads the Browning, preparing another practice run with a confident smile. He used to fire Soviet machine guns. This one, he said, is a massive improvement.

"It's much better because it doesn't fail," he said. "When you fire a Soviet one it often gets jammed after a few shots just because of the dust getting in. With the Browning, even when it jams as you saw, you jerk it and keeps working. No problem," he adds.

While it would be a problem if Western weapons like this one stopped making their way into Ukrainian hands, it's not something Vasyl can afford to worry about.

"Politics is for the politicians," he explained. "My job is here, my job is to fight."

And he say's he'll do so, with US weapons or not.

"We would be able to perform well with a Soviet gun," he said. "We don't have a choice. We have to fight."