BOHDANIVKA, Ukraine — The trenches, the dugouts, the duckboards, the wood-burning stoves, the cold and mud seem to hark back to the First World War.

But not the equipment on Ukraine’s side of the front lines.

Powerful night-vision devices remove the cover of darkness. Counterartillery radar detects and pinpoints the batteries during firing. Surveillance drones, troubled at first by Russian hacking when introduced in 2016, have since proved their worth, Col. Yevhen Bondar said.

It all came from the United States, over the course of five years and part of about $4 billion in military and security assistance designed to counter the Moscow-backed separatist rebellion in eastern Ukraine’s Donbas region.

“It’s helped us significantly,” Bondar said. In the Ukrainian colonel’s view, simply providing an army with modern equipment is in itself a deterrent to an aggressor.

This was the sort of aid that President Trump froze over the summer as he sought to pressure President Volodymyr Zelensky into announcing investigations of former vice president Joe Biden and his son Hunter — although no known evidence of wrongdoing by the Bidens has emerged.

And that freeze is now at the heart of the House impeachment hearings.

The block on a nearly $400 million aid package, approved by Congress, was lifted Sept. 11, in time to beat the end of the federal fiscal year. For its part, Ukraine is spending nearly 5.5 percent of its gross domestic product on defense and security this year, or about $10 billion.

The Trump-ordered delay was felt in Ukraine — but not so much in terms of spot shortages of military materiel, because equipment such as this always moves in fits and starts. The real fallout has been one of perception among Ukrainian officials and others — the worry that the White House cannot always be counted on to be in Kyiv’s corner.

“What I can say is that the aid from the U.S. hasn’t stopped,” said Lt. Lubomyr Loboiko, who serves at a command base in the town of Volnovakha, in the Donetsk region, about 10 miles west of the front-line village of Bohdanivka. “Instructors are working at our training grounds. They were working, and they are working. And we’re exchanging information.”

But even the temporary freeze affects “geopolitical balance,” said Oksana Syroid, the head of the Self Reliance political party. As a senior Ukrainian lawmaker until July, she was a proponent of close ties to the United States and of military restructuring — including greater civilian oversight of the budget and a crackdown on corruption in procurement.

“For Ukraine and for the Ukrainian people, American support is very symbolic,” Syroid said. “The partnership that we have, it’s like an understanding that we are not alone here.”

'No American policy'

Now Russia is trying to upend that understanding.

“Ukraine should not seek its fortunes overseas,” Russian President Vladi­mir Putin said at a news conference in Brazil last week. “ ‘Across the ocean the calf costs half as much, but it is dear to ship it here’ — you know how the Russian saying goes? This is to say that instead of seeking fortunes overseas, you have to turn to your neighbors. This is the right way to do things.”

Putin’s message was a clear reference to Washington. But the United States is not Ukraine’s only donor.

The Ukrainian armed forces were in woeful condition when the war broke out in 2014. There had been little in the way of modernization over the previous 25 years.

European countries and Canada have channeled about $13 billion toward Ukraine since then, focused less on security issues and more on civil society and development.

But they have also offered military assistance to back up the U.S. efforts. Britain has rotated more than 1,300 troops through Ukraine on training missions. Until this year, tiny Lithuania — itself always on guard against Russia — was the main source of lethal aid to Ukraine, donating more than 200 Soviet-era heavy machine guns, hundreds of tons of ammunition and more than 7,000 Kalashnikov assault rifles.

Poland hosted Ukrainian troops for training on its bases. Canada had sent ballistic vests, helmets, first-aid kits, sleeping bags and hospital gear. It has also led a years-long military training effort in western Ukraine.

Zelensky came to office in the spring hoping to find a way to end the war in the east, which has killed more than 13,000 and left a corner of Ukraine effectively out of Kyiv’s control.

Ukraine and Russia swapped 70 prisoners in September and arranged a disengagement in one front-line town in the Donbas. On Monday, the two nations organized the return of three Ukrainian navy boats seized by the Russians a year ago. The Kremlin confirmed Monday that Putin and Zelensky will meet in Paris in December.

But Zelensky’s hand has not been helped by Trump’s military aid holdback and the U.S. president’s evident lack of interest in the war — even as the conflict has been repeatedly mentioned in testimony during the impeachment inquiry, by officials including William B. Taylor Jr., the top U.S. diplomat in Ukraine.

“People in Washington, D.C., know and they speak about this on a daily basis, that there is no American policy, foreign policy, for the moment,” said Oleksiy Melnyk, an analyst at the Razumkov Center, a think tank in Kyiv. “There’s a big mess, and it’s an opportunity for Russia.”

Peace at what price?

Fortunately for Zelensky, Putin is also interested in a resolution. He is likely, though, to exact a price that could include retaining Kremlin influence in eastern Ukraine.

For now, the nearly $400 million in U.S. aid cannot come close to changing the battlefield balance, which is strongly in Russia’s favor, said Alexander Golts, an independent military analyst in Moscow.

“But it has very strong symbolic impact,” he said. Freezing it “was a very bad signal” to the Ukrainians, Golts added.

And Ukraine has no real alternatives to American technological assistance, said Olena Tregub of the Anti-Corruption Committee on Defense, a Kyiv nongovernmental organization. “Apart from the practical application of a modern Western technology, this aid is a symbol of the political support of a Western global power for Ukraine in its fight for independence from Russia and territorial integrity,” she said.

And still more is needed, said Bondar, the colonel who was interviewed at the base in Volnovakha. Two-thirds of his men still have no night-vision goggles.

Reuben Johnson, a military analyst in Kyiv, said Ukraine could also benefit from better data-linked air defenses, more encrypted radio equipment and drones for electronic warfare to match what the Russians have deployed.

When President Trump appeared to withhold almost $400 million in military aid to Ukraine, these are the forces who would have been affected. (Sergey Morgunov for The Washington Post)

In Bohdanivka, at the front-line observation post called “Fazen”— “pheasant” in Ukrainian — the soldiers of the 128th Mountain Infantry Assault Brigade are exhausted and on edge.

They do six-month tours at the front, eating and sleeping in the wooden-frame dugouts that open onto the trenches. Before them stretch fallow fields. A mile or so away, a windbreak of trees, planted in a more peaceful era, blocks the view of the separatist fighters beyond.

Behind the post is a village that once had 70 families. Just seven remain.

Ukrainian officers have told their troops to hold their fire unless under attack. The soldiers see it as a sign of how keen the government in Kyiv is to tamp down the fighting.

Last week, their commander, Col. Yevhen Korostelyov, lost both his feet in an explosion in a nearby village, and a lieutenant was less seriously wounded. Korostelyov died Tuesday.

The army said it was a mine. But the two officers were reportedly on a paved road at the time, and fragments found at the scene suggest that they may have been attacked by an automatic grenade launcher.

In the town of Bohdanivka in the Donetsk Oblast region of Ukraine, these soldiers could be using equipment bought with part of $400 million of U.S. aid. (Sergey Morgunov for The Washington Post)

At the command base in Volnovakha, a soldier who had just come in from Bohdanivka, Pvt. Mykola Dzeman, said he believes the pro-Russian fighters have stepped up their attacks in response to the news of the American aid freeze. Just knowing about the controversy, he said, “emboldens them.”

Lt. Loboiko said the situation along the front is constantly changing.

“Sometimes the enemy uses guided rockets, sometimes small arms,” he said. “Sometimes during the day, sometimes during the dark of the night hours. Sometimes it’s quieter, sometimes it’s more active. But in general, I can’t say that we’re moving toward any kind of cease-fire.”

A soldier shaves on the front line of Ukraine's war with Russian-backed separatists. A $400 million military aid package may help these forces get more weapons. (Sergey Morgunov for The Washington Post)

The Ukrainians do have an important new card.

Under President Barack Obama, Washington held back from sending lethal assistance, out of concern that the United States could get sucked into a proxy conflict with Russia. Trump reversed the decision, and Javelin antitank missiles started to flow.

There are tight restrictions on how they can be used. For now, they are kept away from the front lines. But if Russia decided to push into Ukraine, the Ukrainian military could speed the Javelins into action.

“The Javelin is the best man-portable anti-armor system in the world,” said Ben Hodges, a retired U.S. Army general who handled military assistance for Ukraine while he led forces in Europe between 2014 and 2017. “With the Russians knowing the Ukrainians had that, that obviously was a deterrent.”

Americans trained Ukrainians on the Javelin over the summer, said Air Force Gen. Tod Wolters, the head of U.S. European Command. About 165 members of the Army’s 101st Airborne Division have been deployed to the Yavoriv Combat Training Center in western Ukraine — near the Polish border, about 500 miles from the front lines — since April.

In September, they were joined by more than 200 additional U.S. service members and an international force of 3,700 troops from 14 countries. Together, they carried out Operation Rapid Trident, a two-week training exercise designed to modernize the Ukrainian military and improve its ability to collaborate with Western forces, according to the U.S. military.

Ukrainian special forces also have traveled to Germany to train with American and European counterparts there.

Western military officials say that the Kremlin has been using the conflict in Ukraine as a proving ground for new cyber-tactics and other techniques. Hodges said that the U.S. Army has changed its own strategies for fighting Russia based on what officers learned from the Ukrainians they trained.

“We exchange with each other information about trench warfare, about hybrid war,” Loboiko said. “It’s been very productive.”

Hodges said, for example, that the Americans have learned how the Russians have used “jamming and intercept and targeting of Ukrainian communications and capabilities, use of drones by Russian armed forces.”

Col. Andrii Ahieiev, head of the joint forces press center, said, “If our opponents understand that we have the latest weapons and equipment, then our enemy acts much more carefully.”

At Volnovakha, Bondar said the country cannot just depend on the outside.

“I think Ukrainians need to rely on Ukrainians, not wait,” the colonel said. “Help is very important, but we need to produce something ourselves. A well-trained and well-off army is a powerful argument in negotiations.”

Englund reported from Moscow and Birnbaum from Kyiv. David L. Stern in Kyiv and Dan Lamothe in Washington contributed to this report.