Before the aid influx, “the Ukrainian military was in woeful shape,” said Mariya Omelicheva, a professor of national security strategy at the Pentagon’s National Defense University who specializes in the region.

“There has been a tangible, measurable impact," added Omelicheva, who visited the Ukrainian training center in March. And beyond that, she said, the help created “an immeasurable, psychological impact — that the U.S. has our back."

Now Trump’s aborted aid cutoff — first reported by POLITICO in late August — has mushroomed into a titanic political fight, centered on allegations that the president was using the military assistance as leverage to push Ukraine’s government to investigate former Vice President Joe Biden and his son Hunter. House oversight committees are demanding more data from the White House Office of Management and Budget on when and how the decision to sever the aid arose, including requesting that some documentation be delivered to Capitol Hill by Tuesday.

The military aid program has steadily shifted American support in recent years much more heavily toward security after economic development, loan guarantees and anti-corruption programs defined much of the support following Ukraine's independence from the Soviet Union in 1991.

The U.S. bumped up its military support in 2014, soon after a popular uprising ousted President Viktor Yanukovych, an ally of Russian President Vladimir Putin, and Russian troops annexed the Crimean peninsula while fomenting a separatist uprising in eastern Ukraine's Donbass region.

The vast majority of the funds, approved with bipartisan support in Congress, has financed items such as sniper rifles; rocket-propelled grenade launchers; counter-artillery radars; command and control and communications systems; night vision goggles; medical equipment; as well training and logistical support.

Ukrainian President Volodymyr Zelensky is especially interested in buying more Javelin anti-tank missiles to combat Russian tanks and other armored vehicles — a topic he broached during his July 25 telephone call with Trump that is at the center of the impeachment inquiry.

"Mr. Trump brought up American aid to that country — without explicitly mentioning that he had just frozen a military aid package of hundreds of millions of dollars — and then pressed the Ukrainian leader to investigate Mr. Biden," says the unclassified copy of the whistleblower complaint that the Trump administration released last week. "White House officials believed they had witnessed Trump abuse his power for personal political gain."

The call came a week after Trump ordered his acting chief of staff, Mick Mulvaney, to instruct OMB to halt the remainder of $390 million in military aid appropriated by Congress this year in the Pentagon and State Department budgets. The administration released the aid earlier this month after demands from Congress.

Even before the current furor, questions of how much or how little to help Ukraine's military counter Russian aggression have embroiled Washington for years.

Nowhere was it more pointed than the Ukrainians’ request, as far back as 2014, to purchase the advanced Javelin anti-tank missiles.

The Javelin issue “became fetishized and it became a litmus test: ‘Will you stand up to Putin or will you kowtow to him?’” said Samuel Charap, a former senior adviser at the State Department specializing in Russia and Eurasia. “It was like a Rorschach test.

"It had nothing to do with the merits of the Javelin or the question of what would actually be most effective and important for helping Ukraine," added Charap, who is now a senior political scientist at the government-funded Rand Corp.

The Obama administration agonized over the issue but never approved the sale out of fear of escalating the conflict — despite entreaties from Carter, who served in several top Pentagon positions at the time.

The aim was to “do everything we could within the boundaries of what was wise without baiting the Russians into doing something worse,” recalled Chuck Hagel, the former Republican senator who was Obama's secretary of defense from 2013 to 2015.

The Javelins also helped spur a controversy over the Republican Party's platform in 2016, after Trump’s campaign succeeded in watering down anti-Russia language and ensuring it would not call for “providing lethal defensive weapons” to Ukraine.

Yet once Trump was in office, the Ukrainian government and its allies in Congress kept pushing the request.

Finally, in 2018, long after the Russian tanks pulled back from the front, the State Department finally approved a foreign military sale of 210 Javelin missiles, along with launchers and training, for $47 million.

Charap said the missiles’ military value was limited — they “ended up on the other side of the country from where the conflict is and under lock and key.” But they held significant value in eastern Ukraine, where retired U.S. Army Maj. Gen. John Gronski credits the missiles with helping to stabilize the military crisis by “deterring the separatists from bringing armor into the region.”

The Ukrainians "really appreciate the Javelins,” said Gronski, who served as the deputy commanding general of U.S. Army Europe until June of this year.

Michael Kofman, a senior research scientist at CNA, a government-funded think tank, also called the Javelins an "insurance policy" against Russian escalation.

But in Carter's view, "its political significance was greater than its military significance."

However, the less controversial military aid -- including some of the $390 million dollars slated to go to Ukraine this year from the Pentagon and State Department -- has come to represent a lifeline for the Ukrainian military, which has achieved key milestones in recent months.

And Trump's recent assertion that the aid initiated under Obama has merely provided "sheets and pillows" is directly refuted by those who oversaw it.

The Pentagon, which opposed cutting off the aid this summer, told Congress in May that efforts to help reform the country's military and armaments industry, which has historically been notoriously corrupt, have paid major dividends.

"Through these engagements, the United States has effectively helped Ukraine advance institutional reforms through a number of substantial actions to align Ukraine's defense enterprise more closely with NATO standards and principles," John Rood, the undersecretary of Defense for policy, told oversight committees.

He certified that Ukraine's military "has taken substantial actions" to tackle corruption, improve accountability and is "sustaining improvements to combat capability enabled by U.S. assistance."

That applies especially to the U.S.-financed military training, which takes place at the Yavoriv training center in western Ukraine near the border with Poland.

Initially, American, Polish, Lithuanian and Canadian troops conducted the training of Ukrainian forces — first for smaller, company-sized units of several hundred soldiers and then up to the level of a brigade, which can include thousands of troops.

But now, battle-experienced Ukrainian troops are conducting most of the training, Gronski said, leaving the U.S. forces “in more of an observer role.”

And U.S. instruction in combat medicine has had a direct impact on the battlefield in the east, Gronski said. “Several times, across several visits, Ukrainian battalion commanders told me that those kits and that training absolutely saved lives."

