YAVORIV COMBAT TRAINING CENTER, Ukraine — This summer's delay in releasing nearly $400 million in U.S. aid to Ukraine — allegations at the center of the impeachment proceedings against President Donald Trump— may have been temporary, but the incident is not far from the minds of those training on a wintry base in the west of the country.

Trump’s attempt to pressure Ukrainian President Volodymyr Zelenskiy into investigating former Vice President Joe Biden has also exposed the cracks in the West’s response to an emboldened Russia, inflicted permanent damage on Ukraine and heightened the risk of Moscow extending its influence in the country, according to democracy advocates and military experts.

U.S. support, in particular, is seen as essential in keeping what is widely seen as a bully in the East at bay.

“Just the presence of the American army on the territory of Ukraine, in my opinion, already scares the enemy — even without any other aid,” said Ukraine Ground Forces Sgt. Maj. Yevhen Mokhtan, who works in this multinational training facility in western Ukraine.

The country’s five-year war with Russia has come at a terrible cost: Nearly 13,000 people have been killed in eastern Ukraine, according to United Nations figures. Nearly 430,000 children have been exposed to psychological trauma, and 2 million people are “at risk of death and injury from land mines and other explosive remnants of war,” UNICEF said in a recent report.

To date, the U.S. has committed more than $600 million toward supplying weapons, such as anti-tank missiles, in addition to Humvees, unmanned aerial vehicles, countermortar systems, medical supplies and other equipment to Ukraine. But a key aspect of this “security force assistance” to Ukraine is joint training: honing skills and developing relationships with foreign militaries.

On a cold, early December morning, U.S. soldiers conducted one such joint training exercise with the Ukrainian military. With icy fog in the air, a platoon of soldiers moved toward a small clutch of buildings. One by one, the men ran as comrades fired to suppress the enemies inside.

"Snipers" holed up in those buildings fired potshots at the advancing men. But still the assault platoon advanced, and several squads rushed inside. The crack of rifles and the dull thump of grenades announced their progress.

Ukrainian soldiers take part in a field exercise conducted by the Wisconsin Army National Guard's 32nd Infantry Brigade Combat Team at a training center in Ukraine on Nov. 26. Oksana Parafeniuk / for NBC News

Once a “wounded” soldier was safely recovered, an observer in a bright yellow vest blew a whistle and called the exercise to an end. The soldiers who formed up for a debriefing are from the 93rd Mechanized Brigade, based in Cherkaske in one of Ukraine’s eastern provinces, and will soon redeploy to Donbass, where Ukraine continues to battle Russian-backed separatists.

The brigade has had 138 soldiers killed in action, with nearly 1,000 more wounded during a two-year combat tour from the beginning of the war, until it was pulled off the front-lines in 2016.

The soldiers training for urban combat will soon be risking their lives once again to protect Ukrainian sovereignty. Meanwhile, Ukraine itself is on the front-lines of a wider war, a war over values. And the U.S. military aid is central to that fight.

And as Ukraine teeters between Russia and Western Europe, what is at stake is nothing less than the country’s very soul, according Volodymyr Yermolenko, a professor who runs Ukraine World, an English-language media project aimed at combating disinformation and fake news.

Staff Sgt. Rachael Bannach observes a training exercise in Ukraine on Nov. 26. Oksana Parafeniuk / for NBC News

“The question about military aid to Ukraine is not about Ukraine; it’s about values. It’s about shifting Western liberal democracy eastward,” he told NBC News in Kyiv, the Ukrainian capital, in late November. Yermolenko, an eloquent, gentle-spoken philosopher and academic, has spent years as the driving force behind books and projects intended to educate the world about Ukraine, its history and its post-Soviet struggles.

When the USSR collapsed in 1991, Ukraine and other former Soviet republics were left with broken institutions and economies, which were quickly taken over and plundered by kleptocrats and oligarchs building fortunes from the ruins of the former superpower. Through the late 1990s, Russia itself struggled through economic and political chaos, re-emerging as a global power under President Vladimir Putin’s iron fist.

Amid a vacuum of good governance and political stability in its neighbors, Russia sought to re-establish itself as the center of power amid its former de facto empire. Putin’s ambition is to restore Russia’s influence, which would curtail the spread of liberal democracy, Yermolenko said.

But not everyone was content to again become subordinate to Moscow, he says.

“Ukraine is a country that tries to enlarge these democratic liberal values farther to the East. It's the key, probably, to a future democratizing Russia,” Yermolenko said. “If you don't help Ukraine in this process, you stop democracy moving farther through Eastern Europe, and moreover you can create a situation where rational autocracy would spill over to the West.”

“Now we have this feeling that this international support is kind of fragmenting, and that poses an existential risk for Ukraine,” he said. “Russia never stops.”

The help Washington has provided extends beyond the battlefield: Many citizens have also turned toward the West, hoping to improve their lives and their country.

Daria Kaleniuk leads a meeting at the Anti-Corruption Action Center in Kyiv. Oksana Parafeniuk / Oksana Parafeniuk for NBC News

Daria Kaleniuk studied in the U.S. as a Fulbright scholar, and now seeks to embrace American legal and political systems to reform Ukraine.

“After the collapse of the Soviet Union, Ukraine decided to be a liberal democracy. We decided to build a free market,” said Kaleniuk, who co-founded the Anti-Corruption Action Center, a nonprofit focused on exposing corruption and strengthening apolitical governance and the rule of law. “We decided to build a free society. We decided we don't want any more of an autocratic regime. We wanted to move to the West.”

It is not an easy fight.

Several anti-corruption campaigners in Ukraine have been assassinated, and death threats are common.

“And Russia was always dragging us back.”

Kaleniuk cited the independence of the U.S. legal system as an inspiration for her work.

Reformers like Kaleniuk employ a two-pronged approach to changing the way business and governance are conducted in Ukraine. The first is by changing the country from within by exposing corruption and building the framework for an open legal and political system. The second is seeking support from international organizations and governments, especially in Europe and the U.S.

One of the biggest donors to the anti-corruption campaign was USAID, the U.S. aid agency, Kaleniuk said. “The reason they were doing that is because they have a huge stake of money allocated for good governance, rule of law and anti-corruption reforms in Ukraine,” she said.

However, the gains have been fragile, not least because of Ukraine’s security crisis. Now, with their country at the center of Trump’s impeachment hearings, Ukrainians are concerned about whether U.S. support will continue.

Either way, the withholding of military aid and the request to investigate the Bidens will have far-reaching effects, Kaleniuk predicted.

“The cost of that request was very important, very high,” Kaleniuk said. “It’s in human lives. It’s war.”